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Injuries of the Posterolateral Corner of the Knee

Investigation performed at the Department of Orthopaedic Surgery, Naval Hospital, Bremerton, Washington, and the Department of Surgery, Uniformed Services University of the Health Sciences, Bethesda, Maryland
Captain Dana C. Covey, Medical Corps, United States Navy
Department of Orthopaedic Surgery, Naval Hospital, HP01 Boone Road, Bremerton, WA 98312-1898. E-mail addresses: coveyd{at}pnw.med.navy.mil and dcovey@aol.com. Please address requests for reprints to D.C. Covey.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

	Introduction

Top Introduction Anatomy Functional Biomechanics Mechanism of Injury Natural History Diagnosis Nonoperative Treatment Operative Treatment Overview References

 
The complex anatomy of the posterolateral corner of the knee is due largely to the evolutionary changes in the anatomic relationships of the fibular head, the popliteus tendon, and the biceps femoris muscle.

Recent research has improved our understanding of the popliteus complex, particularly the role of the popliteofibular ligament.

Biomechanical studies provide a scientific basis for clinical examination of the knee with suspected injury of the posterolateral corner.

All grade-I and most moderate grade-II injuries of the posterolateral structures can be treated nonoperatively, but residual laxity may remain, especially in knees with grade-II injury.

Acute grade-III isolated or combined injury of the posterolateral corner is best treated early, by direct repair, if possible, or else by augmentation or reconstruction of all injured ligaments.

Chronic injury of the posterolateral corner, whether isolated or combined, is probably best treated by reconstruction of the posterolateral corner along with reconstruction of any coexisting cruciate ligament injury.

Failure to diagnose and treat an injury of the posterolateral corner in a patient who has a known tear of the anterior or posterior cruciate ligament can result in failure of the reconstructed cruciate ligament.

Injuries of the posterolateral corner of the knee are infrequent but can cause severe disability due to both instability and articular cartilage degeneration^1-3. These injuries do not usually occur in isolation but are often associated with injury of the anterior or posterior cruciate ligament^4,5. The diagnosis of subtle lesions of the posterolateral corner can be elusive unless there is a high degree of clinical suspicion for possible injury of this region. The consequence of missing a posterolateral injury in the presence of a known tear of the anterior or posterior cruciate ligament can be failure of the reconstructed cruciate ligament^6-8. Recent studies have shed new light on the complex anatomy and functional mechanics of the posterolateral corner of the knee, and they provide a framework for improved diagnosis and treatment of these often disabling injuries.

	Anatomy

Top Introduction Anatomy Functional Biomechanics Mechanism of Injury Natural History Diagnosis Nonoperative Treatment Operative Treatment Overview References

 
The posterolateral corner of the knee, with its complicated and varying anatomy of static and dynamic stabilizers, is probably the least understood region of the knee; it was once considered the "dark side" of the knee⁹. The inconsistent terminology used to describe the structures in the posterolateral corner has added to the confusion^10,11. This is underscored by the varying nomenclature applied to the popliteofibular ligament, which has been called the short external lateral ligament¹², the popliteofibular fascicles¹³, the fibular origin of the popliteus¹⁴, the popliteus muscle with origin from the fibular head¹¹, and the popliteofibular fibers¹⁵. In fact, because of an oversight, mention of this structure disappeared from standard anatomy texts and the orthopaedic literature during the middle of the twentieth century, only to be rediscovered recently¹⁶.

Evolutionary and Developmental Anatomy
To conceptualize the morphology of the posterolateral corner, an understanding of the evolutionary and developmental anatomy helps to explain some of the confusing structural relationships.

The complex anatomy of the posterolateral corner of the knee is due largely to the evolutionary changes in the anatomic relationships among the fibular head, the popliteus tendon, and the biceps femoris muscle¹⁷. In paleontologic specimens dating back 360 million years, in extant lower vertebrates, and in early human embryonic development, both the fibula and the tibia articulate with the femur^18-20. However, as the vertebrate knee evolved, the fibula and the attached lateral portion of the joint capsule moved distally to form a new capsular layer between the distal part of the femur and the proximal popliteus muscle, resulting in the popliteal hiatus and an intra-articular popliteus tendon. In early evolution, when the fibula articulated with the femur, the popliteus tendon inserted on the fibular head. With subsequent distal migration of the fibular head, the popliteus tendon acquired a femoral attachment while retaining its original fibular insertion¹⁷. There also was an evolutionary change in the location of the biceps femoris tendon attachment, from the lateral aspect of the capsule and the proximal part of the tibia to the fibula²¹.

The major components of the posterolateral corner of the knee appear early in the course of human development. Between seven and eight weeks of embryonic development, the fibular head has completed its distal migration to reach a definitive location with respect to the proximal part of the tibia, and the lateral collateral ligament, popliteus tendon, and lateral meniscus are identifiable^22-24. At eight weeks, the embryonic knee has assumed a shape similar to that of the adult joint; three weeks later, the popliteofibular ligament can be seen, having formed during the process of fibular migration, with the attached popliteus tendon. By the sixteenth week of development, the connections among the popliteus tendon, the lateral meniscus, and the fibular head that are seen in the adult knee are fully formed²⁴.

Macroscopic Anatomy
The major structures of the posterolateral corner of the knee include the iliotibial tract, the lateral collateral ligament, the popliteus complex consisting of both dynamic components (the popliteus muscle-tendon unit) and static components (the popliteofibular ligament, popliteotibial fascicle, and popliteomeniscal fascicles), the middle third of the lateral capsular ligament, the fabellofibular ligament, the arcuate ligament, the posterior horn of the lateral meniscus, the lateral coronary ligament, and the posterolateral part of the joint capsule^14,16,17,25. This anatomy can be quite variable.

In their study of thirty-five cadaver knees, Seebacher et al.²⁵ described the lateral structures of the knee as comprising three distinct layers (Fig. 1Fig. 1). The most superficial layer consists of the iliotibial tract, including its anterior expansion, and the superficial portion of the biceps and its expansion posteriorly. The middle layer is formed by the quadriceps retinaculum anteriorly but is incomplete posteriorly, being represented by the two patellofemoral ligaments. It also contains the patellomeniscal ligament. The third and deepest layer forms the lateral part of the joint capsule. This layer is divided into a superficial lamina, which encompasses the lateral collateral ligament and ends at the fabellofibular ligament, and a deep lamina, which forms the coronary ligament and the popliteal hiatus, terminating at the arcuate ligament. The popliteofibular ligament is a component of this deep layer. Seebacher et al. noted three anatomic variations in their knee dissections. The arcuate ligament alone reinforced the posterolateral part of the capsule in 13% of the knees, the fabellofibular ligament alone reinforced it in 20%, and both reinforced it in 67%.

Fig. 1: An axial depiction of the posterolateral corner of the knee shows the three-layer anatomy. (Reprinted from: Seebacher JR, Inglis AE, Marshall JL, Warren RF. The structure of the posterolateral aspect of the knee. J Bone Joint Surg Am. 1982;64:537.)

In a study of 115 cadaver knees, Watanabe et al.¹¹ identified seven anatomic variants by including the presence or absence of what they termed the popliteus muscle with origin from the fibular head (the popliteofibular ligament) in a classification scheme that also included the variability of the arcuate and fabellofibular ligaments previously noted by Seebacher et al.²⁵. They found a lateral collateral ligament and a popliteus tendon in all knees and a popliteofibular ligament in 94%. Terry and LaPrade¹⁷ recently performed dissections of thirty cadaver knees to provide a detailed description of the complex anatomy and to develop a dependable operative approach to the posterolateral structures. They used this operative approach in a series of seventy-one patients and noted that it provided excellent access for inspection and repair of injured components of the posterolateral corner of the knee.

Blood Supply
The blood supply to the posterolateral corner of the knee comes from named and unnamed branches of the popliteal artery. The lateral superior genicular artery is divided into three branches. The articular branch supplies the lateral collateral ligament and the lateral region of the knee. This branch anastomoses with the ascending branch of the lateral inferior genicular artery that runs anteriorly, deep to the lateral collateral ligament^17,26. The middle genicular artery provides an important contribution to the posterior capsular region²⁷. Additional contributions come from the posterior tibial recurrent artery that ramifies into small branches to supply the popliteus muscle, the tibial condyle, and the joint area superior to the fibular head²⁶. Small branches off of the popliteal artery also supply the posterior capsular region²⁶.

Innervation
The posterolateral structures of the knee are innervated from several sources. With contributions from the posterior articular nerve (a prominent branch of the posterior tibial nerve) and from the terminal portions of the obturator nerve, the popliteal plexus supplies the posterolateral part of the capsule and the external portion of the lateral meniscus^28,29. The terminal portion of the nerve to the vastus lateralis supplies the superior portion of the lateral part of the capsule. The lateral articular nerve arises from the common peroneal nerve and innervates the inferior portion of the lateral part of the capsule and the lateral collateral ligament^28,30.

The knee contains complex mechanoreceptors that play an important role in proprioceptive reflex arcs. Ruffini endings, found in the capsule, menisci, and ligaments, are slowly adapting static and dynamic mechanoreceptors that signal static joint position; changes in intra-articular pressure; and the direction, amplitude, and velocity of knee movements^30,31. Pacinian corpuscles and Golgi-tendon organ-like endings have also been identified in meniscal, capsular, and ligamentous tissues. The former rapidly adapt to signal joint acceleration and deceleration, while the latter are high-threshold, slowly adapting mechanoreceptors that are activated when high stresses are generated in ligaments or when the knee is at the extremes of motion^30,31. Free nerve-endings, which are widely distributed throughout most of the articular tissues, are high-threshold, nonadapting pain receptors that respond to mechanical deformation or inflammatory mediators^30,31. Any injury of the posterolateral structures affects not only knee kinematics but also afferent signals to the central nervous system.

	Functional Biomechanics

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Much of our knowledge of how each component of the posterolateral corner of the knee contributes to stability comes from biomechanical studies in which changes in primary and coupled motions have been measured. Primary translations and rotations occur along the axis of the applied force or moment, whereas coupled translations and rotations do not^10,32.

With use of selective ligament sectioning in cadaver knees, Nielsen et al.^33-36 demonstrated the importance of the posterolateral structures in resisting excessive varus and external rotation forces. The lateral collateral ligament and the posterolateral part of the capsule resisted varus and external rotation of the tibia, with the former having a greater role against a varus moment and the latter, a greater role against external rotation torque³⁵. The popliteus tendon resisted excessive external rotation of the tibia during knee flexion from 20° to 130°, and it resisted excessive varus rotation of the tibia during flexion from 0° to 90°³⁴. Combined sectioning of the lateral collateral ligament and the posterolateral part of the capsule resulted in more posterolateral instability than did isolated cutting of either structure³⁶. The posterolateral structures also served as secondary restraints to posterior translation, and isolated sectioning of the posterior cruciate ligament did not affect varus or external rotation stability^33,35.

Gollehon et al.³⁷ also investigated the static contributions of the posterolateral structures to joint stability in cadaver knees and expanded upon the findings of Nielsen et al. They selectively transected the lateral collateral ligament, the anterior and posterior cruciate ligaments, and what they termed the popliteus-arcuate (deep) ligament complex consisting of the arcuate ligament, popliteus tendon, fabellofibular ligament, and posterolateral part of the joint capsule^10,37. In the range of motion from 0° to 90°, the lateral collateral ligament and the deep ligament complex were the principal structures preventing varus and external rotation of the tibia, while the posterior cruciate ligament was the principal structure resisting posterior translation. Isolated sectioning of either the lateral collateral ligament or the deep ligament complex did not increase posterior translation, but their combined sectioning caused small increases in posterior translation throughout the range of motion. Isolated sectioning of the lateral collateral ligament caused a small increase (from 1° to 4°) in varus rotation at all angles, but when it was combined with sectioning of the deep ligament complex, varus increased further throughout the range of motion and was greatest at 30°. Additional sectioning of the posterior cruciate ligament resulted in larger increases (from 15° to 19°) in varus rotation. Sectioning of the deep ligament complex increased primary external rotation at 90° of flexion, but when it was combined with sectioning of the lateral collateral ligament, primary rotation and coupled external rotation increased at all angles and were maximal at 30°. When the posterior cruciate ligament was also sectioned, there were additional increases in posterior translation and varus rotation at all flexion angles, and primary external rotation increased with flexion greater than 30°. Isolated sectioning of the posterior cruciate ligament did not affect varus rotation or external rotation at any knee angle. When the anterior cruciate ligament was sectioned along with the lateral collateral ligament and the deep ligament complex, tibial internal rotation and anterior translation increased at 30° and 60° of flexion. Isolated sectioning of the anterior cruciate ligament or combined sectioning of the lateral collateral ligament and the deep ligament complex did not increase internal rotation of the tibia.

Although the experimental protocols varied, subsequent biomechanical studies were in general agreement that isolated sectioning of the posterolateral structures increased primary varus rotation, primary external rotation, primary posterior translation, and coupled external rotation^38-42. Markolf et al.⁴⁰ further demonstrated that, after complete sectioning of the posterolateral structures, tibial varus or external rotation caused an increased force in the posterior cruciate ligament between 45° and 90° of flexion. An applied posterior force on the tibia combined with external rotation significantly increased (p < 0.05) the force in the posterior cruciate ligament at all angles except full extension. Although internal rotation had no effect on the posterior cruciate ligament, it did increase the force in the anterior cruciate ligament between 0° and 20° of flexion. With use of defined loading conditions, Noyes et al.⁴¹ quantified the abnormal increases in posterior subluxation of the tibial plateau that occurred after specific ligament sectioning. Cutting of the posterolateral structures increased posterior translation of the lateral tibial plateau at 30° but not at 90° of flexion. Combined sectioning of the posterolateral structures and the posterior cruciate ligament increased posterior subluxation of both the medial and the lateral tibial plateau at 30° and 90° of flexion.

Recent research has also advanced our understanding of the popliteus complex, particularly the popliteofibular ligament (Fig. 2Fig. 2). Veltri et al.⁴² performed a cadaveric sectioning study that was similar to that by Gollehon et al.³⁷ except that it specifically included the popliteofibular ligament. The results of these two studies were similar, since the popliteofibular ligament may have been sectioned as part of the deep ligament complex in the earlier study. Veltri et al.⁴² found that primary external rotation of the tibia was not increased by combined sectioning of the anterior cruciate ligament and the posterolateral corner, an observation that differed from that of Wroble et al.⁴³, who documented increases in external rotation in the same experimental situation. Subsequently, Veltri et al.⁴⁴ examined the static contributions of the popliteus complex to knee stability by selectively cutting the lateral collateral ligament, the popliteofibular ligament, and the popliteus tendon attachment to the tibia. They found that the latter two structures were important in resisting posterior translation, primary varus rotation and external rotation, and coupled external rotation. Shahane et al.⁴⁵ also found that the popliteofibular ligament had an important role in preventing excessive posterior translation, varus rotation, and primary and coupled external rotation. Maynard et al.¹⁶ found that the popliteofibular ligament had a cross-sectional area that was only slightly smaller than that of the lateral collateral ligament, and it had an average maximal force to failure of 425 N compared with 747 N for the lateral collateral ligament. Hoher et al.⁴⁶ examined the effects of posterior tibial loading on the popliteus complex and the lateral collateral ligament in cadaver knees before and after sectioning of the posterior cruciate ligament. They found that these structures play an important role in resisting posterior forces at full extension, and, when the posterior cruciate ligament is sectioned, at all angles.

Fig. 2: Arising from the posterior part of the fibula (asterisk), the popliteofibular ligament joins the popliteus tendon just superior to the musculotendinous junction. (Reprinted, with permission, from: Veltri DM, Warren RF. Anatomy, biomechanics, and physical findings in posterolateral knee instability. Clin Sports Med. 1994;13:602.)

Skyhar et al.⁴⁸ recorded articular contact pressures in ten cadaver knees with use of pressure-sensitive film and a model that simulated non-weight-bearing, resistive extension of the knee. They showed that combined sectioning of the posterolateral complex and the posterior cruciate ligament resulted in significantly more patellofemoral joint contact pressure than did isolated sectioning of the posterior cruciate ligament (p < 0.05).

Clinical Relevance
The findings of these biomechanical studies provide a scientific basis for examination of suspected posterolateral injury of the knee. An isolated tear of the posterior cruciate ligament does not increase primary varus rotation or primary external rotation but does cause increased posterior translation of the tibia that increases with knee flexion. The most accurate means of diagnosing such an injury is the posterior drawer test with the knee flexed 90°⁴⁹. An isolated tear of the lateral collateral ligament causes a mild increase (1° to 4°) in varus angulation that is maximal at 30° of knee flexion; thus, adduction stress-testing should be performed at this angle. Injury of all posterolateral structures, with an intact posterior cruciate ligament, results in maximally increased varus, external rotation, and posterior translation at 30° of flexion. These increases in motion occur since only 10% to 15% of the posterior cruciate ligament's fibers are relatively taut at low knee-flexion angles and thus are unable to effectively resist these motions^50,51. However, at 90° of flexion, all fibers of the intact posterior cruciate ligament are tight and are able to exert an effective secondary restraint against a varus moment or external rotation torque and to exert a primary restraint against posterior translation^38,40,52. When a complete injury of the posterolateral corner is combined with an injury of the posterior cruciate ligament, the primary and secondary restraining effects of a tight posterior cruciate ligament are lost at high knee-flexion angles. Consequently, there is increased posterior translation, varus rotation, and external rotation at all angles of knee flexion. When isolated or combined posterolateral corner injury is suspected, stress tests for increased varus rotation and external rotation should be performed at 30° and 90° of flexion and compared with the results for the uninjured knee¹⁰. A combined anterior cruciate ligament and posterolateral corner injury increases primary anterior and posterior translation, primary varus, coupled external rotation, and probably primary internal rotation^42,43. There is disagreement as to whether the external rotation test at 30° of flexion is reliable for detecting combined anterior cruciate ligament and posterolateral complex injury^42,43. The biomechanical data also support the clinical observation that cruciate ligament grafts are at risk for failure in knees with untreated posterolateral rotatory instability⁶.

	Mechanism of Injury

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Isolated injury of the posterolateral complex is relatively uncommon. DeLee et al.⁵³ reported that, of 735 knees that were treated for ligament injuries, only twelve (1.6%) had acute isolated posterolateral instability. Athletic trauma, motor-vehicle accidents, and falls are the most common causes of injury of the posterolateral corner of the knee^5,53-58. Isolated posterolateral injury can result when a posterolateral force is directed against the proximal part of the tibia with the knee at or near full extension^1,53. This mechanism produces knee hyperextension combined with a varus moment to disrupt the posterolateral structures^54,55,59. Other mechanisms can cause injury of the posterolateral corner in combination with injuries of other ligaments. These include a combined hyperextension and external rotation force, contact and noncontact hyperextension, a severe varus bending moment, and a severe tibial external rotation torque^54,58,60,61. Another possible mechanism of combined injury occurs when the knee is flexed and the tibia is externally rotated and a posteriorly directed force is then applied to the tibia. In this situation, tension in the posterior cruciate ligament is markedly decreased compared with that seen with neutral tibial rotation because the posterolateral structures are recruited to resist the applied force⁶². The posterolateral complex is then prone to injury, and, given enough force, the posterior cruciate ligament would also be injured. A complete dislocation of the knee can also cause severe injury of the posterolateral corner structures^56,58,63.

	Natural History

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There is little published information on the long-term natural history of nonoperatively treated injuries of the posterolateral corner of the knee. Furthermore, there are no reports, to my knowledge, on the natural history of isolated injury of individual components of the posterolateral complex. Lesions of the ligamentous structures of the posterolateral corner are often classified as grade-I, II, or III sprains (injuries) depending upon whether there is minimal, partial, or complete tearing of the ligament^2,61,64,65. Grade-I injuries are not associated with abnormal joint motion, grade-II injuries are associated with slightly to moderately abnormal joint motion, and grade-III injuries are usually associated with markedly abnormal joint motion^32,64. Many authors have used a numerical scale of 1+, 2+, and 3+ to further delineate the amount of ligamentous instability^1,2,21,53,54. Hughston et al.¹ and Baker et al.⁵⁴ used this scale qualitatively to describe ligamentous instability as mild (1+), moderate (2+), or severe (3+). Others have quantitated the amount of joint opening with a defined stress as 1+ (0 to 5 mm with a definite end point), 2+ (6 to 10 mm with a definite end point), or 3+ (greater than 10 mm with a soft or no appreciable end point)^21,53.

Kannus² followed twenty-three patients who had been treated nonoperatively for a grade-II or grade-III sprain of the posterolateral complex. At an average of eight years after the injury, the eleven patients with a grade-II sprain had an excellent or good result as assessed with standardized scales, nine were asymptomatic, and all had residual laxity. However, the twelve patients with a grade-III sprain had a much worse result, and the average scores on standardized grading scales were either fair or poor. Eight of these patients also had had a partial tear of the anterior cruciate ligament or the posterior cruciate ligament, or both, and two patients had had a previous lateral meniscectomy, so this subgroup cannot be viewed as having had a strictly isolated posterolateral injury. Six of the twelve patients with a grade-III injury had posttraumatic arthritis on radiographic evaluation, but no patient with a grade-II injury had arthritic changes.

In a study in which the follow-up ranged from six months to thirteen years, Krukhaug et al.⁵ found that all of their six patients with a lateral ligament injury who had had mild (1+) varus instability treated by early mobilization had a stable knee.

	Diagnosis

Top Introduction Anatomy Functional Biomechanics Mechanism of Injury Natural History Diagnosis Nonoperative Treatment Operative Treatment Overview References

 
History
The initial step in the evaluation of a possible injury of the posterolateral corner of the knee is to obtain a thorough history. Patients with acute isolated injury of the posterolateral corner usually complain of pain in the posterolateral aspect of the knee, and some may have neurologic symptoms as well. Injury of the peroneal nerve was present in two of twelve patients with isolated injury of the posterolateral corner in the series of DeLee et al.⁵³ and in two of seventeen patients with such an injury evaluated by Baker et al.⁵⁴. Recent reports by LaPrade and Terry⁶¹ and by Krukhaug et al.⁵, on patients with posterolateral knee injury, including those with combined lesions, showed prevalences of peroneal nerve injury of 13% of seventy-one patients and of 16% of twenty-five, respectively.

Patients with chronic posterolateral injury may describe medial joint-line pain, lateral joint-line pain, and posterolateral pain^1,4,61. They may also have paresthesias, numbness, or weakness from an injury of the common peroneal nerve. Patients frequently have functional instability when the knee is in extension, which limits the type and intensity of their activities. This instability may include the knee giving way into hyperextension during activities such as ascending and descending stairs or slopes and instability with twisting, pivoting, or cutting maneuvers⁴. Hughston et al.¹ coined the term posterolateral rotatory instability to describe posterior subluxation of the lateral tibial plateau that can occur with an external rotation torque in knees with pathologic laxity of the posterolateral corner. Symptoms of posterolateral rotatory instability can occur acutely after severe injury, or they can develop insidiously after a relatively mild posterolateral injury.

Physical Examination
Injuries of the posterolateral structures of the knee are commonly associated with other ligamentous lesions and may be missed at the time of the initial evaluation^60,66,67. The knee should be carefully examined for edema, ecchymosis, induration, and tenderness⁵⁴. DeLee et al. ⁵³ found that patients with acute posterolateral corner injury had diffuse tenderness over the posterolateral joint region, with point tenderness localized over the fibular head or at the joint line in patients with arcuate⁶⁸ or Segond⁶⁹ fracture, respectively. LaPrade and Terry⁶¹, in their series of seventy-one patients, noted arcuate fracture in three patients and Segond fracture in one patient. Abrasion, laceration, or ecchymosis in the region of the tibial tubercle should raise the suspicion of concomitant injury of the posterior cruciate ligament⁷⁰. Tears or avulsions involving the posterolateral structures can be part of a constellation of knee injuries that have occurred as a consequence of a spontaneously reduced dislocation of the knee^71,72. If a knee dislocation is suspected, a thorough neurovascular examination is essential and an arteriogram may be appropriate^73,74.

Patients with a suspected posterolateral corner injury should be carefully observed for limb alignment and changes in their gait. Patients may present with a standing varus alignment of the knee, and an abnormal gait pattern characterized by a varus thrust or a hyperextension varus thrust may develop during the stance phase^75,76. To avoid the pain and instability of knee hyperextension, some patients may walk with a slightly flexed knee⁵⁵. Increased knee flexion, seen in the midstance phase of gait in some patients with combined posterolateral and posterior cruciate instability, could be a mechanism to avoid secondary stresses on the joint and the posterior part of the capsule that are greater in full extension⁷⁷. Some patients with marked posterolateral knee injury may be able to actively reproduce the instability (voluntary posterolateral drawer sign)⁷⁸.

Examination is carried out to ascertain the functional integrity of specific structures, and comparison is made with the uninjured knee. A posterior drawer test should be performed at 30° and 90° of knee flexion. If posterior translation is slightly increased at 30° but is normal at 90°, posterolateral injury should be suspected. The status of the posterior cruciate ligament is most commonly determined by the posterior drawer test performed at 90° of knee flexion^37,38,66,79, but it can also be assessed by other methods, including evaluation for the posterior sag sign, the prone posterior drawer test, the quadriceps active test, the reverse pivot-shift test (which may be positive in up to 35% of normal knees examined under anesthesia⁸⁰), and the dynamic posterior shift test⁴⁹. Hughston⁸¹ reported, however, that not all patients with posterior cruciate injury have a positive posterior drawer test on physical examination. The status of the anterior cruciate ligament can be assessed by the Lachman test⁸². A number of specific tests to help diagnose injuries of the posterolateral corner of the knee have been described. To increase accuracy, patients with a concomitant tear of the posterior cruciate ligament should have any posterior subluxation reduced while the posterolateral aspect of the knee is evaluated, either while they are in the prone position or with the examiner maintaining the tibia in a reduced position while they are supine.

Tibial external rotation (dial) test: This test can be performed with the patient either prone or supine; however, the prone position may be easier for documenting side-to-side differences in the thigh-foot angle^76,83. The test should be performed at both 30° and 90° of knee flexion because increased external rotation at 30° but not at 90° indicates an isolated injury of the posterolateral corner, whereas increased external rotation at both angles suggests injury of both the posterior cruciate ligament and the posterolateral corner. To quantitate tibial rotation, Bleday et al.⁸⁴ used an electronic goniometer to help in the diagnosis of injuries of the posterolateral aspect of the knee. They presented data on side-to-side differences in external rotation in 180 uninjured knees at both 30° and 90° of flexion. The efficacy of this device awaits further study. External rotation of the tibia that exceeds that of the uninjured limb by 10° or more suggests posterolateral corner injury⁸⁵.

Posterolateral external rotation test: The results of this combination of the posterior drawer and external rotation tests have correlated with injury of the lateral collateral ligament⁶¹. It is performed with the knee flexed to both 30° and 90°, with application of a coupled posterior translation and external rotation force to the proximal part of the tibia and palpation for posterolateral subluxation of the tibia. Subluxation at 30° but not at 90° indicates an isolated injury of the posterolateral corner of the knee, whereas subluxation at both angles suggests combined posterior cruciate ligament and posterolateral injury.

Reverse pivot-shift test: Jakob et al.⁸⁶ reported that this test is positive if there is a sensation of reduction when the flexed, externally rotated knee is extended with valgus stress. The test may indicate injury of the posterior cruciate ligament and the posterolateral complex, but it may be positive in up to 35% of normal knees examined under anesthesia⁸⁰.

External rotation recurvatum test: This test, described by Hughston et al.^1,87, is used to diagnose posterolateral rotatory instability in the extended knee. It is performed by lifting the patient's legs by the great toes and noting any side-to-side differences in hyperextension, varus, and tibial external rotation.

Posterolateral drawer test: Hughston and Norwood⁸⁷ reported on a specific type of posterior drawer test in which the knee is flexed 80° and the foot is externally rotated 15° in order to assess the displacement and external rotation of the lateral tibial plateau. In a study of 100 normal knees examined under anesthesia, Cooper⁸⁰ found that the results of this test were variable and difficult to quantify and that there was not always a firm end point. Jacobson²⁸ recently recommended that the test be performed at 30° and 90° of knee flexion to distinguish between isolated posterolateral corner injury and that combined with a posterior cruciate ligament tear. Patients with a combined injury would likely have an increased posterolateral drawer at both knee-flexion angles, whereas those with an isolated posterolateral injury would have a positive test at 30° only.

Dynamic posterior shift test: Shelbourne et al.⁸⁸ characterized this test as a reliable adjuvant to other tests for posterior and posterolateral injury. With the patient supine, the examiner flexes the patient's hip and knee to 90° and then passively extends the knee until a jerk or clunk is felt when the subluxated tibia suddenly reduces as the knee nears full extension. With straight posterior instability both tibial plateaus move forward equally, but with posterolateral instability the lateral plateau is pulled back farther and increased tibial rotation is seen with reduction.

Standing apprehension test: Ferrari et al.⁸⁹ reported that a positive test results from tibiofemoral displacement that occurs while the patient stands with the affected knee slightly flexed and the examiner's thumb pushes on the anterolateral part of the lateral femoral condyle. Movement of the condyle relative to the tibial plateau can be palpated while the patient experiences a giving-way sensation.

Veltri and Warren⁷⁶ reported that the most useful tests for the diagnosis of posterolateral knee injury were the prone external rotation test at 30° and 90° of flexion and the varus stress test at 0° and 30° of flexion. For the diagnosis of posterolateral instability, they utilized other tests such as the reverse pivot-shift test and the external-rotation recurvatum test, to supplement their clinical impression.

Imaging Studies
Radiographs of a knee with posterolateral injury may show abnormal widening of the lateral joint space, an arcuate fracture of the fibular head, avulsion of the Gerdy tubercle off of the tibia, or a Segond fracture (lateral capsular sign), which is an avulsion of the lateral aspect of the capsule from the tibial plateau^5,53,75. Although the latter sign is usually considered indicative of a tear of the anterior cruciate ligament, it also occurs in association with isolated posterolateral injury because the midlateral part of the capsule is quite strong and large forces can cause avulsion of metaphyseal bone^25,53. Patients with chronic posterolateral injury have radiographic changes consistent with arthritis of the medial or lateral compartment or with patellofemoral arthritis^1,90.

In some cases, particularly acutely injured, painful knees for which it is difficult to perform an optimal physical examination, magnetic resonance imaging can help in the diagnosis of posterolateral corner injury^91-94. Yu et al.⁹⁵, in a cadaver and clinical study, showed that coronal oblique T2-weighted magnetic resonance images provided better visualization of the structures of the posterolateral corner of the knee than did standard coronal or sagittal images. In a recent prospective study of twenty patients with a grade-III injury of structures of the posterolateral corner (seven patients with an acute injury and thirteen with a chronic injury), LaPrade et al.⁹⁶ developed a protocol that specifically included the entire fibular head and styloid process on all magnetic resonance imaging sequences. They found that most of the individual components of the posterolateral aspect of the knee, as well as acute and chronic injuries of these structures, could be accurately visualized with their technique. A related finding by Ross et al.⁹², in their small series of six knees with combined injury of the posterolateral complex and the cruciate ligaments, was the presence of a bone contusion of the anteromedial femoral condyle on magnetic resonance imaging in all cases.

Arthroscopic Examination
Arthroscopy has also been found to be useful in the diagnosis of injuries of the posterolateral corner of the knee. Staubli and Birrer¹³ performed an arthroscopic evaluation of the lateral compartment and popliteal hiatus in forty knees with an acute tear of the anterior cruciate ligament and twenty-eight knees with a chronic tear. They identified structural lesions of the popliteus complex in 95% of the acutely injured and 86% of the chronically injured knees. In a prospective study of thirty knees with a grade-III injury of the posterolateral corner of the knee (five had isolated posterolateral injury and twenty-five, combined ligamentous injury), LaPrade⁹⁷ found that arthroscopy was valuable in diagnosing lesions of individual structures in the lateral compartment when it was performed concurrently with open reconstruction. Some injuries might have gone undetected if only open operative treatment had been performed. LaPrade noted that an increased amount of lateral joint laxity could be appreciated arthroscopically as a so-called drive-through sign. Arthroscopy does pose a risk of fluid extravasation in an acutely injured knee with major capsular damage.

	Nonoperative Treatment

Top Introduction Anatomy Functional Biomechanics Mechanism of Injury Natural History Diagnosis Nonoperative Treatment Operative Treatment Overview References

 
Nonoperative treatment of grade-I or II injury of the posterolateral corner can have a good outcome^2,5. In one small group of seven patients with mild (1+) varus instability, the six patients treated with early mobilization had a stable knee but the one patient treated with immobilization in a cast had residual mild varus instability⁵.

Nonoperative treatment of complete tears involving the posterolateral corner of the knee has generally led to poor functional results². Patients who have chronic posterolateral instability often have quadriceps atrophy and associated gait abnormalities that may include a variable degree of knee hyperextension, and this may reflect isolated posterolateral or combined ligamentous injury⁷⁵. Because the altered gait mechanics are likely to produce forces that adversely affect the articular surfaces of all three compartments of the knee, formal gait instruction may be beneficial. A program consisting of gait-retraining and comprehensive muscle rehabilitation decreased pain and improved function in a small series of patients with combined posterolateral and cruciate ligament injuries, but reconstructive surgery is usually necessary in active patients⁹⁸.

	Operative Treatment

Top Introduction Anatomy Functional Biomechanics Mechanism of Injury Natural History Diagnosis Nonoperative Treatment Operative Treatment Overview References

 
Operative procedures for the treatment of lesions of the posterolateral corner of the knee can be broadly categorized as primary repair, augmentation, and advancement and reconstruction.

Acute Injury of the Posterolateral Corner of the Knee
Operative treatment of acute lesions of the posterolateral corner of the knee is generally more successful than is surgery for chronic posterolateral injury^{4,5,53,54,56,58-60}. When grade-III injuries of the posterolateral corner are diagnosed acutely, direct anatomic repair of all injured structures within three weeks has the highest likelihood of giving the patient an optimal result^{5,28,60,65,75,94,99}. Arthroscopy performed before open repair facilitates the diagnosis of lateral compartment injury and allows treatment of any associated meniscal or cruciate ligament pathology^13,97. Cruciate ligament reconstruction is indicated when a tear is present, and it is usually performed before repair or reconstruction of the posterolateral structures^5,28,97,98.

The posterolateral corner of the knee can be adequately exposed through a lateral hockey-stick-shaped, straight, or curvilinear incision^4,57,100,101. An operative approach through the injured structures has been recommended, but this requires a thorough understanding of the anatomic relationships to be accomplished safely¹⁷. Terry and LaPrade¹⁷ described three fascial incisions and one lateral capsular incision that provide access to the individual components of the posterolateral corner, but they noted that it was rarely necessary to use all four incisions in the same knee. Major structures that should be evaluated during the exposure include the iliotibial tract, biceps femoris, peroneal nerve, lateral collateral ligament, popliteus muscle and tendon, and popliteofibular ligament¹⁰¹. Treatment of posterolateral injuries should proceed from deep to superficial, with repair of structures by direct suture, sutures via drill-holes through bone, or suture anchors as appropriate^28,94. In the acute situation where the severity of injury precludes direct repair, involved structures can be augmented with hamstring tendon, biceps femoris tendon, iliotibial band, or allograft^28,75,101.

Chronic Injury of the Posterolateral Corner of the Knee
Chronic injury of the posterolateral corner of the knee usually presents a more complex problem than acute injury because of extensive scarring, secondary changes to other structures, and possible limb malalignment. The goals of operative treatment include restoration of knee stability and kinematics, a return to preinjury activity levels without pain or instability, and a reduction of the likelihood or severity of long-term knee arthrosis. Reconstructive procedures can be broadly classified as those that are intended to reproduce the normal anatomy of the region or as those that are meant to stabilize the posterolateral corner by tightening specific tissues. When a grade-III injury of the posterolateral corner is associated with other ligamentous tears, there is a general consensus that combined operative intervention offers the potential for a better outcome than does treatment of an isolated injury^{6,7,28,60,65,90,102}. There is a lack of consensus in the literature on the best technique of operative treatment. This is a reflection of the low prevalence of posterolateral injury, the various ways of measuring the results of treatment, differences in the nature and chronicity of injury, and variations in postoperative rehabilitation.

In cases of marked varus alignment and a lateral thrust in the stance phase of gait, consideration should be given to performing a valgus tibial osteotomy as an initial procedure to prevent excessive loads on the lateral capsular structures that are to be reconstructed^65,101,103. Full-length weight-bearing radiographs of both lower extremities can aid in evaluating the overall limb alignment. In patients with chronic posterolateral instability and valgus alignment of the lower limb, the pathology of the posterolateral corner is directly addressed¹⁰¹. Noyes et al.⁹⁸ found that preoperative gait-training was a useful adjunct to reconstructive surgery in patients with chronic combined cruciate and posterolateral knee injuries.

Hughston and Jacobson⁴ followed ninety-five patients (ninety-six knees) for an average of four years after anterior and distal advancement of the osseous attachment of the arcuate ligament complex (the lateral gastrocnemius tendon, lateral collateral ligament, and popliteal tendon). Of these ninety-six knees, 85%, 78%, and 80% were rated as good objectively, subjectively, and functionally. This technique does not address injury to the popliteofibular ligament or the popliteus musculotendinous junction, and it also moves the attachments of the lateral collateral ligament and the popliteus tendon anterior and distal to their normal locations⁹⁰, which could result in progressive attenuation of these structures.

Noyes and Barber-Westin¹⁰⁰ reported the results in twenty-one patients with combined posterolateral and cruciate ligament injuries after proximal advancement of the posterolateral complex and cruciate ligament reconstruction. Their procedure was modified from that of Hughston and Jacobson⁴ in that the tissue was advanced with the knee in 30° rather than 90° of flexion and the lateral collateral ligament was fixed at its normal anatomic attachment^100,104. The posterolateral advancement was fully functional in 64% of the patients, partially functional in 27%, and nonfunctional in 9% at an average of forty-two months postoperatively. Noyes and Barber-Westin emphasized that the posterolateral structures must have sufficient intact collagenous tissue and that, if poorly organized scar tissue or tissue without adequate distal attachment is advanced, the procedure will fail. These investigators^57,75 also used Achilles tendon allograft or bone-patellar tendon-bone autograft to reconstruct the lateral collateral ligament, and they used autogenous hamstring tendon to reconstruct the popliteus complex in combination with plication or advancement of the posterolateral structures as indicated. Of twenty-one patients who were followed for an average of forty-two months postoperatively, 76% had a good-to-excellent functional result and 10% had failure of the reconstruction⁵⁷.

Clancy and Sutherland¹⁰⁵ reported that tenodesis of the biceps femoris tendon to the lateral femoral epicondyle could negate the deforming force of the biceps femoris muscle and create an approximation of the lateral collateral ligament. Thirty-nine patients with chronic posterolateral rotatory instability, usually from combined cruciate ligament and posterolateral injuries, were followed for an average of thirty-two months after this procedure¹⁰⁶. The authors found that 77% of the patients had no restrictions in their activities of daily living and that 54% were able to return to their previous competitive level in sports. Factors associated with inferior results were degenerative changes involving the knee joint and receipt of Worker's Compensation. Fanelli et al.¹⁰⁷ also used the biceps tenodesis procedure along with arthroscopically assisted reconstruction of the posterior cruciate ligament to treat combined injury of the posterolateral complex and the posterior cruciate ligament in twenty-one patients. At a minimum of two years postoperatively, all patients had either correction or overcorrection of the posterolateral instability as measured by the tibial external rotation test. A study in cadaver knees showed that biceps tenodesis could be effective in statically eliminating abnormal external rotation and varus rotation, but it did so by overconstraining these motions³. Whether initial static overconstraint in vivo would remain or attenuate over time to produce a normal or pathologic laxity pattern is not known. Veltri et al.⁴⁴ noted that biceps tenodesis did not reproduce the popliteofibular ligament or popliteus tendon attachment to the tibia, both of which are important stabilizers.

Jakob and Warner¹⁰⁸ suggested that recession of the popliteus and lateral collateral ligaments into the lateral femoral condyle can restore tension yet maintain the anatomic attachment sites. This procedure would be appropriate in cases of mild attenuation when the popliteus musculotendinous junction and the popliteofibular ligament are intact (Fig. 3Fig. 3). Depending upon the amount of attenuation, this reconstruction may be augmented with other tissue.

View larger version (144K): [in this window] [in a new window]   Fig. 3: The intraoperative appearance of the femoral attachments of the popliteus tendon (left) and the lateral collateral ligament (right) in the left knee. Both structures are in continuity but show attenuation and scarring from chronic injury (arrows).

Veltri and Warren⁷⁶ recommended that all injured posterolateral structures be anatomically reconstructed. A lateral collateral ligament with a chronic tear can usually be reconstructed with a distally based section of biceps femoris tendon (Fig. 4Fig. 4) or, alternatively, with autograft or allograft⁷⁶. For tears that involve the popliteus complex, both the tibial and the fibular (popliteofibular ligament) attachments of the popliteus tendon should be addressed. With isolated injury of either the tibial or the fibular component of the popliteus complex, the surgeon can use a single graft fixed within the lateral femoral condyle that extends distally through a tunnel in the tibia or fibula, respectively (Fig. 5Fig. 5). In cases where both the tibial and the fibular component of the popliteus complex are torn, a single split Achilles-tendon allograft or patellar tendon autograft or allograft can be used. With this technique, the graft bone-plug is fixed in the lateral femoral condyle; the graft is split distally and then passed through tunnels in the proximal parts of the tibia and fibula (Fig. 5Fig. 5). Bullis and Paulos¹¹⁰ used a similar technique employing a bifid Achilles-tendon allograft to reconstruct the popliteus complex.

Fig. 4: Anatomic reconstruction of the lateral collateral ligament with a central section of the biceps femoris tendon. (Reprinted, with permission, from: Veltri DM, Warren RF. Operative treatment of posterolateral instability of the knee. Clin Sports Med. 1994;13:621.)

Fig. 5: Reconstruction of the popliteus. Left: reconstruction of the tibial attachment of the popliteus and the popliteofibular ligament with a split patellar tendon graft. (Achilles tendon allograft can also be used.) The graft is fixed in the lateral femoral condyle, and its bifid distal ends are secured in the tibial and fibular tunnels. Right: isolated reconstruction of the popliteofibular ligament with a graft. (Reprinted, with permission, from: Veltri DM, Warren RF. Operative treatment of posterolateral instability of the knee. Clin Sports Med. 1994;13:625.)

Potential complications associated with the operative treatment of posterolateral corner injuries include peroneal nerve injury during the operative approach or reconstruction, wound problems such as infection and hematoma, loss of knee motion postoperatively, failure of the reconstruction, and irritation from hardware used in the reconstruction^28,83.

	Overview

Top Introduction Anatomy Functional Biomechanics Mechanism of Injury Natural History Diagnosis Nonoperative Treatment Operative Treatment Overview References

 
New studies on the anatomy and biomechanics of the posterolateral corner of the knee are helping to refine the treatment of these injuries. The preponderance of basic research shows that each component of the posterolateral complex is important for proper functioning of the knee. All grade-I and most moderate grade-II injuries of the posterolateral structures can be treated nonoperatively, but residual laxity may remain, especially in patients with a grade-II injury. Acute grade-III isolated or combined injury of the posterolateral corner of the knee is best treated early (within three weeks) by direct repair if possible, or else by augmentation or reconstruction of all injured ligaments. Chronic injury, whether isolated or combined with other tissue injury, is probably best treated by reconstruction of the posterolateral corner along with reconstruction of any coexisting cruciate ligament injury. A number of operative techniques have been devised to treat posterolateral injuries, but most have achieved only modest success. With our redefined understanding of the complex morphology of the posterolateral aspect of the knee, it appears that anatomic reconstruction, with use of modern techniques that restore normal tibiofemoral stability and kinematics, offers the best potential for long-term excellent results. However, determination of the efficacy of anatomic reconstruction awaits the outcomes of long-term clinical studies.

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