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Brace-Free Rehabilitation, with Early Return to Activity, for Knees Reconstructed with a Double-Looped Semitendinosus and Gracilis Graft*

LIEUTENANT COLONEL STEPHEN M. HOWELL, and CAPTAIN MICHAEL A. TAYLOR, , MEDICAL CORPS, UNITED STATES AIR FORCE RESERVE

Investigation performed at the Clinical Investigation Facility, David Grant Medical Center, Travis Air Force Base

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
Forty-one patients in whom operative reconstruction of a torn anterior cruciate ligament had been performed by one surgeon with use of a double-looped semitendinosus and gracilis hamstring graft were studied to determine (1) if a brace-free rehabilitation program compromised the early stability of the knee; (2) if the stability of the knee deteriorated between four months, when the patient returned to unrestricted activities, and two years; and (3) if the function of the treated knee was completely restored by four months after the operation. The graft was placed arthroscopically, without impingement by the intercondylar roof, and was fixed within the tibial tunnel to conserve the length of the graft. The stability and function of thirty-seven of the knees were assessed at four months as part of a larger prospective study. Four patients chose not to return for the four-month evaluation. The patients returned to unrestricted sports and work activities after the four-month evaluation. At two years, all forty-one patients were evaluated. At four months, after completion of the brace-free rehabilitation program, thirty-three (82 per cent) of the thirty-seven patients had an absent pivot shift and a normal Lachman test. Twenty-eight (88 per cent) of thirty-four knees had less than three millimeters of difference in laxity compared with the contralateral knee, as determined by testing at the maximum manual force with use of a KT-1000 arthrometer. Stability remained unchanged at two years, justifying the early return to vigorous activities at four months. The girth of the thigh, the extension of the knee, and the Lysholm and Gillquist score were the same at four months as at two years, verifying the success of the brace-free intensive rehabilitation program in the restoration of early function to the treated knee. However, some continued improvement was observed in the performance of the one-leg-hop for distance test between four months and two years.

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion References

 
The two structures that are most commonly used for autogenous grafts in the reconstruction of a torn anterior cruciate ligament are the patellar ligament and the hamstring tendons. Most surgeons prefer the patellar ligament because it is readily procured, can be fixed firmly, and tolerates the loads produced by an intensive rehabilitation program. Patients who have a patellar ligament autogenous graft can return to vigorous activities two to six months after the operation without affecting the stability of the knee at two years after the operation^8,23,24. However, there are concerns that the same rapid rehabilitation may not be successful with the use of other graft materials¹⁷. To our knowledge, the outcome of an intensive rehabilitation program and an early return to sports and work activities for patients who have had a reconstruction of the knee with the use of hamstring tendons has not been reported.

This observational study was designed to measure the function and stability of knees that had been reconstructed with a double-looped semitendinosus and gracilis hamstring graft. A functional assessment and arthrometric measurements of stability were made at four months, after completion of a brace-free, intensive rehabilitation program, and at two years after the operation. The objectives of the study were to determine (1) if the rehabilitation program compromised the early stability of the knee, (2) if the stability of the knee deteriorated after the patients returned to unrestricted activities at four months, and (3) if the function of the knee was completely restored by four months after the operation.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion References

 

Patients
Forty-nine consecutive operations were performed by the senior one of us (S. M. H.), from February 1991 to May 1992, with the use of a four-bundle graft consisting of a loop of the semitendinosus and a loop of the gracilis tendon to replace a torn anterior cruciate ligament. Only knees that were available for follow-up after two years were included in the study. Eight patients were excluded because they did not return for the two-year evaluation (Table I). The most recent stability measurements for four of these patients were recorded four to thirteen months after the operation; one of the four died fourteen months postoperatively, two were re-evaluated by telephone three years after the operation, and one was lost to follow-up. The most recent stability measurements for three other patients were recorded at two months; one of these patients had an unstable knee, and two were re-evaluated by telephone approximately four years after the operation. The remaining patient was lost to follow-up after one month.

Thirty-four patients had had no operation on the knee before the index procedure. Six patients had had one previous operation. Four of them had had an arthroscopic partial medial meniscectomy; one, an arthroscopic medial and lateral meniscectomy; and one, an arthroscopic débridement. One patient had had two previous operations: an open repair of the medial collateral ligament and an arthroscopic débridement. Twenty-five index procedures were performed within six months after the injury, and sixteen were performed after six months. Two patients had a tear of the medial collateral ligament.

All of the patients had an attenuated anterior cruciate ligament diagnosed preoperatively and confirmed intraoperatively. Preoperatively, stability was determined objectively with a KT-1000 arthrometer (MedMetric, San Diego, California) at an applied anterior load of eighty-nine newtons and with a maximum manual anterior force. The difference in anterior displacement between the injured and contralateral knees was calculated. All of the injured knees had at least three millimeters more anterior laxity than the contralateral knee, which is diagnostic of an attenuated anterior cruciate ligament^5,6. Subjectively, the end point on Lachman testing was soft in all injured knees. Intraoperatively, thirty-nine knees had a fully positive pivot shift and, during arthroscopy, all of the anterior cruciate ligaments were observed to be attenuated or absent.

The forty-one patients returned for evaluation at a mean of twenty-six months (range, twenty-four to thirty-two months) after the index operation. To control for examiner bias, the one of us who did not perform the operations (M. A. T.) independently examined thirty-seven patients at the most recent evaluation. Because of scheduling conflicts, the senior one of us evaluated the remaining four patients. Stability and functional data were also available for thirty-seven patients at four months postoperatively. These data were obtained from a larger prospective study in which information was collected preoperatively and at one, two, and four months after the procedure by the senior one of us.

Functional Assessment
The patients categorized their level of activity before the injury, after the injury but before the operation, and two years after the operation. They chose one of four categories. Strenuous activities included sports that required jumping, pivoting, and hard cutting maneuvers, such as football, soccer, and basketball; moderate activities included those that required strenuous manual work, such as skiing, tennis, baseball, and volleyball; light activities included those that required light manual work, such as jogging, running, and cycling; and sedentary activities included housework and desk jobs with no participation in sports.

The girth of the thigh five and fifteen centimeters proximal to the superior pole of the patella as well as the extension of the knee were measured on the treated and contralateral sides. The difference between the girth of the thigh of the treated limb and that of the contralateral limb was calculated, and the girth of the thigh of the treated limb was assigned to one of four categories: (1) at least two centimeters greater than that of the contralateral limb, (2) within one centimeter of that of the contralateral limb, (3) two centimeters less than that of the contralateral limb, or (4) more than two centimeters less than that of the contralateral limb. The difference in extension of the knee was also calculated and the extension of the treated knee was assigned to one of three categories: (1) hyperextension equal to that of the contralateral knee, (2) hyperextension not equal to that of the contralateral knee, and (3) extension to 0 degrees.

The patients performed a one-leg-hop for distance test by standing on one limb, hopping as far as possible, and landing on the same limb. The distance was measured and recorded. Alternating between the treated and the contralateral limb, each limb was tested three times. The hop index was the mean distance hopped by the treated limb divided by the mean distance hopped by the contralateral limb, with the result multiplied by 100. A hop index of 85 per cent or more was considered normal⁴.

The Lysholm and Gillquist score was used to assess the subjective function of the knee, with the help of the patient. Points were assigned for the level of function within several categories: degree of limp; level of weight-bearing; ability to climb stairs and to squat; degree of atrophy of the thigh; and sensation of instability, pain, or swelling during walking, running, or jumping. The score for a normal knee is 100 points.

The International Knee Documentation Committee form was used to evaluate the function of the knee at the most recent follow-up examination⁷. Knees were graded as normal (A), nearly normal (B), abnormal (C), or severely abnormal (D) in seven categories: the patient's assessment of the function of the knee, symptoms (such as pain, swelling, and giving-way), motion, stability, crepitus in each knee compartment, morbidity at the donor site, and the one-leg-hop for distance test. The lowest grade in any category was used as the final result for that knee. The grade for a normal knee is A.

Assessment of Stability
Three tests were used to evaluate the stability of the reconstructed knee. The result of the Lachman test for the treated knee was graded as having either a firm or a soft end point. The result of the pivot-shift test was assessed by comparison of the degree of rotatory subluxation in the treated knee with that in the contralateral knee. The difference in the KT-1000 displacement values between the treated and the contralateral knee was calculated. Anterior displacement was recorded to the nearest 0.5 millimeter with the knee in 20 to 30 degrees of flexion at two different loads. An eighty-nine-newton load was applied with use of the force handle on the arthrometer, and a maximum manual anterior translation was measured by manual application of a high anterior force to the proximal aspect of the calf just distal to the knee joint line.

Stability was determined with the combined results of the Lachman test, the pivot-shift test, and the arthrometric laxity measurements. A stable knee had three findings: a firm end point, no pivot shift or a subtle pivot glide equal to that of the contralateral knee, and a difference of less than three millimeters between the anterior displacement of the treated knee and that of the contralateral knee during a maximum manual force. An unstable knee had a soft end point, an increased pivot shift compared with that of the contralateral knee, or an increase in anterior displacement of three millimeters or more.

Roentgenographic Assessment
We previously described a measurement technique to determine the percentage of impingement by the intercondylar roof, the location of the central axis of the tibial tunnel, and the slope of the intercondylar roof^11-13. These measurements were performed on a lateral roentgenogram of the fully extended knee, made at the most recent follow-up examination (Fig. 1).

View larger version (113K): [in this window] [in a new window]   The percentage of impingement by the intercondylar roof, the location of the center of the tibial tunnel, and the slope of the intercondylar roof were determined from several landmarks on the lateral roentgenogram of the fully extended knee. The plane of the tibial plateau was defined by line AB. The center of the tibial tunnel (CTT, arrow) bisected the distance from the anterior edge of the tibial tunnel (AETT) to the posterior edge of the tibial tunnel (PETT). The slope of the intercondylar roof was defined as the angle subtended by the line of the slope of the intercondylar roof (IR, dotted line) and the long axis of the femur.

The location of the central axis of the tibial tunnel was calculated by extension of the line of the central axis of the tibial tunnel to its intersection with the line of the tibial plateau; the distance from this intersection to the anterior end of the line of the tibial plateau was then measured. This distance was divided by the length of the line of the tibial plateau, and the result was expressed as a percentage^11,13,16.

The slope of the intercondylar roof was measured as the angle subtended by the line of the slope of the intercondylar roof and the long axis of the femur^11,13,16.

Complications
A review of the chart and consultation with the patient at the most recent follow-up examination were used to determine the occurrence of complications. Complications were divided into those associated with procurement of the graft and those related to the intra-articular portion of the operation. The potential morbidity that is associated with procurement of the graft includes wound infection, superficial phlebitis, deep-vein thrombosis, loss of sensation in the skin overlying the proximal-lateral aspect of the tibia due to injury to the infrapatellar branch of the saphenous nerve, and weakness during flexion of the knee. The potential morbidity associated with the intra-articular portion of the operation includes infection, arthrofibrosis, prominence of the hardware, and the need for an additional operation.

Operative Technique
The senior one of us previously described the intra-articular, arthroscopically assisted reconstruction of the anterior cruciate ligament with use of a double-looped semitendinosus and gracilis autogenous graft by means of a two-incision technique⁹.

Briefly, the semitendinosus and gracilis tendons were procured with a tendon-stripper (Acufex Microsurgical, Norwood, Massachusetts). Retained muscle was removed, and sutures were sewn to each end of each tendon. The mid-point of each tendon was looped over a single suture. The suture was used to pull the four-bundle graft through a series of calibrated cylinders (Arthrotek, Ontario, California). The diameter of the snuggest-fitting cylinder defined the diameter of the four-bundle graft and was used to select the diameter of the cannulated reamer to drill the tibial and femoral tunnels. The four-bundle graft was seven, eight, or nine millimeters in diameter. Four knees (10 per cent) were treated with a seven-millimeter graft; twenty-eight knees (68 per cent), an eight-millimeter graft; and nine knees (22 per cent), a nine-millimeter graft.

Of the thirty-six knees that had not had a previous operation on the medial meniscus, nine had a partial excision of that structure and five had an arthroscopic suture repair; three knees had an incomplete tear that was left alone. Eight of the forty knees that had not had a previous operation on the lateral meniscus had a partial excision of that structure; an incomplete tear was left alone in three other knees.

A previously described technique^9,10,13,14 was used to customize the placement of the tibial tunnel to account for variability in extension of the knee and the slope of the intercondylar roof among the knees¹¹ and to avoid impingement by the roof. With use of a guide system (Impingement-Free Tibial Guide System; Arthrotek), the center of the tibial tunnel was positioned four to five millimeters posterior and parallel to the slope of the intercondylar roof with the knee in maximum extension within the posterior half of the insertion of the anterior cruciate ligament. The tibial tunnel was drilled, and bone was removed from the intercondylar roof and wall. Elimination of impingement by the roof was confirmed when a metal rod (Impingement-Free Tibial Guide System), the same diameter as the graft, could be advanced freely through the tibial tunnel into the intercondylar notch with the knee in full extension (Fig. 2). The center of the femoral tunnel was positioned five to seven millimeters distal to the proximal edge of the intercondylar roof, at the eleven o'clock orientation for the right knee or the one o'clock orientation for the left knee, with use of a rear-entry or front-entry femoral guide system (Acufex Microsurgical). The femoral tunnel was drilled through the lateral incision.

View larger version (38K): [in this window] [in a new window]   Illustration demonstrating how bone was removed from the wall and roof of the intercondylar notch until a metal rod of the same diameter as the graft could be freely advanced into the notch with the knee in maximum extension. The elimination of impingement by the roof was confirmed before the tendon graft was inserted into the knee.

To satisfy our concerns regarding fixation, we devised a method to anchor short grafts as well as longer grafts consistently without a suture bridge. The length of the graft was conserved by looping the mid-point of each tendon around a fixation post (a 4.0-millimeter-diameter small-fragment cancellous-bone screw; Synthes, Paoli, Pennsylvania) countersunk inside the tibial tunnel. A drilling device (Tibial Fixation Device; Arthrotek) positioned the fixation post twenty millimeters inside the tibial tunnel, as measured from the distal end of the tunnel⁹ (Fig. 3). The smooth section of the screw spanned the bore of the tibial tunnel while the threaded section gained purchase in the cancellous metaphysis and the posterior cortex of the tibia (Fig. 4). The graft was inserted so that the free ends of each tendon extended outside the femoral tunnel while the mid-point of each tendon was looped around the recessed screw. With the knee in full extension, an unmeasured tension was applied manually to the free ends of the tendons exiting the femoral tunnel. The graft was secured to the lateral femoral cortex in thirty-nine knees with one or two 6.5-millimeter cancellous-bone screws and ligament washers (Synthes). In two knees, two soft-tissue staples (Stryker, Kalamazoo, Michigan) were used because the ligament washers were unavailable. Fragments produced by the reaming of the bone were impacted into the tibial tunnel with an impingement rod to fill any voids between the tendon, screw, and tunnel wall.

View larger version (54K): [in this window] [in a new window]   Illustration demonstrating how a drilling device was inserted into the tibial tunnel to drill a 2.7-millimeter-diameter hole perpendicular to the long axis of the tibia. The drill-hole bisected the cross section of the tibial tunnel and was located twenty millimeters inside the tunnel, as measured from the distal end of the tunnel. This allowed the graft to be fixed within the tibial tunnel, which conserved the length of the graft.

View larger version (33K): [in this window] [in a new window]   Illustration demonstrating how the smooth section of the screw spanned the tibial tunnel and the threaded section had purchase in the posterior cortex of the tibia. The mid-point of both tendons was looped around the tibial fixation post, and the free ends were secured to the lateral femoral cortex with one or two cancellous-bone screws and a soft-tissue washer. Pieces of bone, saved from the reaming of the tunnels, were packed into the distal end of the tibial tunnel between the tendons and the wall of the tibial tunnel.

Rehabilitation Program
The postoperative regimen included application of a soft dressing, which was kept on for forty-eight hours; continuous passive motion for the first twenty-four to forty-eight hours after the operation; toe-touch weight-bearing for three weeks followed by walking without crutches after three weeks; unrestricted closed and open-chain knee-extension exercises beginning at four weeks; resumption of running in a straight line at eight to ten weeks; and an unrestricted return to sports and work activities at four months. No braces were used.

Analysis of the Data
A paired Student t test was used to compare continuous data at the four-month and two-year follow-up examinations. The Wilcoxon signed-rank test was used when repeated comparisons of ordinal data were required. The Fisher exact test was used when 2 x 2 comparisons of nominal data were appropriate. To determine the percentage of knees that had improved or worsened between four months and two years, paired differences were calculated for the girth of the thigh, the extension of the knee, and the instrumented laxity measurements.

The interobserver analysis of the instrumented laxity measurements was performed with use of the contralateral knee because its anterior laxity was assumed to remain constant over time. This is in contrast to the anterior laxity of the treated knee, which could have increased over time as a result of remodeling of the graft. A paired Student t test was used to compare the maximum manual anterior translation measured in the contralateral knee by the senior one of us at four months with that measured by the other one of us at two years. The four knees examined by the senior one of us at two years were excluded from this analysis.

	Results

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Functional Assessment
The level of sports activity was significantly improved by the operation (p = 0.009) but was not restored to the pre-injury level (p = 0.01) (Table II). Thirty-eight (93 per cent) of the forty-one patients had returned to either strenuous (twenty-five patients; 61 per cent) or moderate (thirteen patients; 32 per cent) activities by two years after the operation.

View larger version (20K): [in this window] [in a new window]   Graph of the percentage of thirty-seven knees with a change in the girth of the thigh between four months and two years. A positive difference indicates that the measurement of girth was larger at two years than at four months. A negative difference indicates that the measurement was larger at four months than at two years. The measurements were made at five and fifteen centimeters proximal to the superior pole of the patella. The four-month and two-year measurements made five centimeters were within one centimeter of each other for 78 per cent (twenty-nine) of the knees and those made at fifteen centimeters were within one centimeter of each other for 73 per cent (twenty-seven) of the knees.

View larger version (18K): [in this window] [in a new window]   Graph of the percentage of thirty-seven knees with a change in extension between four months and two years. A positive difference indicates that more extension was measured at two years than at four months. A negative difference indicates that more extension was measured at four months than at two years. The four-month and two-year measurements were equal for 57 per cent (twenty-one) of the knees, were within 3 degrees of each other for 89 per cent (thirty-three), and were within 6 degrees of each other for 97 per cent (thirty-six).

With use of the International Knee Documentation Committee form, twenty-six (63 per cent) of the treated knees were rated as normal (A); eleven (27 per cent), as nearly normal (B); and four (10 per cent), as abnormal (C) at the time of the most recent follow-up.

Assessment of Stability
The interobserver analysis of the instrumented laxity measurements was performed with use of the results of the maximum manual test on the contralateral, uninjured knee. With the numbers available, we could detect no significant difference between the measurements made at four months (by the senior one of us) (average [and standard deviation], 10.4 ± 1.9 millimeters) and those made at two years (by the other one of us) (average [and standard deviation], 10.2 ± 2.1 millimeters) (p = 0.50). The anterior laxity measured at two years was equal to that measured at four months for sixteen (43 per cent) of the thirty-seven knees examined at both four months and two years, was within one millimeter for thirty (81 per cent), and was within two millimeters for thirty-four (92 per cent) (Fig. 7).

View larger version (21K): [in this window] [in a new window]   Graph of the results of the interobserver analysis of the instrumented laxity measurements. The anterior translation measured, with the maximum manual test, in the contralateral knee at four months (by the senior one of us) was compared with that measured at two years (by the other one of us). Measurements were made in the contralateral knee because its anterior laxity was assumed to remain constant over time. A positive difference indicates that more laxity was measured at two years than at four months. A negative difference indicates that more laxity was measured at four months than at two years. The four-month and two-year measurements were identical for 43 per cent (sixteen) of the knees, were within one millimeter of each other for 81 per cent (thirty), and were within two millimeters for 92 per cent (thirty-four).

View larger version (22K): [in this window] [in a new window]   Graph of the percentage of thirty-seven knees with a change in anterior laxity between four months and two years. A positive difference indicates that more anterior laxity was measured, with the eighty-nine-newton or maximum manual test, at two years than at four months. A negative difference indicates that more anterior laxity was measured at four months than at two years. The four-month and two-year measurements were identical for 32 per cent (twelve) of the knees, were within one millimeter of each other for 73 per cent (twenty-seven), and were within two millimeters of each other for 92 per cent (thirty-four) when the maximum manual test was used.

Two knees that were originally classified as unstable by the senior one of us at four months were reclassified by the other one of us as stable at the most recent follow-up evaluation. This reclassification can be explained by the interobserver variability in arthrometric measurements of laxity. For example, a patient who has a two-millimeter increase in anterior laxity has a 38 per cent chance of having either a one or a three-millimeter increase when re-examined by another observer. Therefore, it is to be expected that some knees may be reclassified when measurements are made by different observers.

At four months, the senior one of us classified the two knees as unstable because of a three-millimeter increase in anterior laxity and despite a firm end point on Lachman testing and an absent pivot shift. At two-years, the other one of us found only a 2.0 and 2.5-millimeter increase in anterior translation, indicating that these knees were stable. As both authors agreed that the two knees had a firm end point on Lachman testing and an absent pivot shift, and because there is variability in measurements of laxity between observers, it seemed justified to reclassify these two knees as stable. Instability thus occurred in four (10 per cent) of the forty-one knees.

With the numbers available, we could detect no significant difference in the over-all rate of instability between the twenty-five patients who had been treated within six months after the injury of the anterior cruciate ligament and the sixteen patients who had been treated more than six months after the injury (p = 0.63).

Roentgenographic Assessment
Impingement by the roof was eliminated in thirty-nine (95 per cent) of the forty-one knees, as the anterior border of the tibial tunnel was in line with or posterior to the intersection of the line of the slope of the intercondylar roof with the plane of the articular surface of the tibial plateau. Two knees, both stable, were classified as having mild impingement¹³, with 10 and 20 per cent of the width of the tibial tunnel lying anterior to this intersection. The slopes of the intercondylar roof averaged 37 ± 5 degrees but ranged from 26 to 44 degrees. The locations of the central axis of the tibial tunnel averaged 38 ± 5 per cent of the sagittal depth of the tibia, with a wide range (30 to 54 per cent).

Complications
Two patients had a superficial wound infection in the tibial incision, which was treated in the office with incision and drainage of the wound and at home with changes of the dressing and oral administration of an antibiotic. Four patients had superficial phlebitis involving the saphenous vein that presented within two weeks after the index operation. Treatment consisted of local application of heat and oral administration of a non-steroidal anti-inflammatory agent. Almost all patients had anesthesia in a several-square-centimeter area of the skin overlying the proximal-lateral aspect of the tibia due to injury of the infrapatellar branch of the saphenous nerve. There were no symptomatic neuromas. One patient had weakness during flexion of the knee. Seven of the forty-one patients had an additional operation: five had removal of all screws and the washer, one had partial excision of the medial meniscus after a failed repair, and one had a lateral release because of pain in the anterior aspect of the knee. No patient needed a manipulation for stiffness. There were no cases of arthrofibrosis or intra-articular infection.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
This study was designed to determine if knees reconstructed with a four-bundle graft, composed of a loop of semitendinosus and gracilis tendon, could be safely and effectively rehabilitated without a brace and with the patient returning to vigorous activities four months after the operation. A high rate of instability and poor clinical function at four months would have indicated that the operative technique and rehabilitation program had been poorly designed. An increase in instability between four months and two years would have implied that the composite hamstring graft was not mature enough to tolerate the early return to sports and work activities. An improvement in the functional assessment of the knee between four months and two years would have shown that the rehabilitation ineffectively restored early function to the knee. A high rate of failure at two years would have suggested that a four-bundle hamstring graft was ineffective for replacement of a torn anterior cruciate ligament.

Thirty-seven (90 per cent) of the forty-one treated knees in this study were stable and functional at two years. The knees that were unstable were detected at the four-month follow-up examination.

An analysis of the possible causes for the early failure of the graft in the four patients was not revealing. The rate of failure was higher in the female patients (two of thirteen) than in the male patients (two of twenty-eight); however, because of the low rate of instability, this difference was not significant. The timing of the operation and the condition of the menisci were not implicated; two operations were performed early and the menisci were intact, and two operations were performed later with one meniscus in each knee being partially excised. The operative procedure was consistent; impingement by the roof was avoided in each knee, and there were no intraoperative difficulties. Each patient complied with the postoperative regimen, and none had a reinjury during the rehabilitation phase. Other possible causes for early failure of the graft that were not measured include variability in the pretensioning of the graft; geometric differences between knees, which may have affected kinematics; and subtle variability in placement of the femoral tunnel, which may have affected the tension of the graft. We were unable to determine a specific cause for the early instability.

The stability of the treated knees did not deteriorate between four months and two years, implying that the grafts were mature enough at four months to stabilize the knees effectively. Studies in which an autogenous patellar ligament graft was used as a replacement for the anterior cruciate ligament have also shown that stability is not affected by a return to vigorous activities as early as two to six months⁸ or four to six months²⁴ after the reconstruction. Collectively, these studies provide substantial clinical evidence that autogenous graft material used to reconstruct the anterior cruciate ligament in humans is strong and mature enough at four months for the patient to return to sports and work activities safely.

The rate of stability of the knees that had been reconstructed with a double-looped hamstring graft in the present study matched the rate of stability reported in two studies^3,24 and exceeded that reported in five studies^1,2,8,20,22 in which an autogenous patellar ligament graft was used to replace the anterior cruciate ligament. Therefore, the double-looped hamstring graft can be used instead of a patellar ligament graft when the goal is an early return to vigorous activities.

One explanation for the success of the double-looped hamstring graft is that it has superior mechanical properties compared with a ten-millimeter-wide patellar ligament graft. The average diameter of the double-looped hamstring graft in our study was eight millimeters, which provides a circular graft with a cross-sectional area of fifty square millimeters. The patellar ligament graft is 3.5 to 4.0 millimeters thick and rectangular¹⁹. A ten-millimeter-wide patellar ligament graft has a cross-sectional area of only thirty-five to forty square millimeters. Normal anterior cruciate ligaments are an average of five millimeters thick and ten millimeters wide and have an average cross-sectional area of fifty square millimeters²¹, which is identical to that of the double-looped hamstring graft. The failure strength of the double-looped graft, as calculated from data reported by Noyes et al., is 238 per cent that of the normal anterior cruciate ligament. The failure strength of a ten-millimeter-wide patellar ligament graft is only 138 per cent that of the normal anterior cruciate ligament. The cross-sectional area of the double-looped hamstring graft more closely approximates that of a normal anterior cruciate ligament, and the hamstring graft has a greater margin of strength than the patellar ligament graft. Thus, it is an excellent autogenous graft for reconstruction.

The operation involved two principles that may have been important to its success. First, impingement of the graft by the intercondylar roof was avoided, which allowed the knees to regain extension easily without the roof abrading and injuring the graft^12-14,16. The technique for prevention of impingement by the roof required that the position of the tibial tunnel be customized to account for the variability, among the knees, in the slope of the intercondylar roof and the extension of the knee¹¹. The slope of the intercondylar roof in the patients in the present study ranged from 26 to 44 degrees, with the center of the tibial tunnel ranging accordingly from 30 to 54 per cent of the sagittal depth of the tibia. The adequacy of the so-called roofplasty and wallplasty was determined before the graft was implanted by insertion of a metal rod, the same diameter as the graft, through the tibial tunnel and into the intercondylar notch with the knee in maximum extension.

The second principle was that firm fixation should be achieved in every knee by conservation of the length of the graft through fixation of the graft within the tibial tunnel. This technique of countersinking the graft was developed because, in our experience^13-15, approximately 20 per cent of the gracilis tendons were too short to be directly fixed to bone outside both tunnels. In the present study, the graft was looped around a fixation post within the tibial tunnel, shifting the point of fixation on the tibia four to five centimeters proximally. In every knee, a long, thick piece of the graft exited the femoral tunnel, allowing firm fixation of the graft directly to the lateral femoral cortex with a cancellous-bone screw and washer.

In summary, the results of this study support the use of a double-looped semitendinosus and gracilis hamstring graft as an alternative to an autogenous patellar ligament graft when intensive rehabilitation of the knee without a brace and a return to sports or work activities four months after the operation are desired.

	Footnotes

 
*One or more of the authors has received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund, foundation, educational institution, or other non-profit organization with which one or more of the authors is associated.

The views expressed in this article are those of the authors and do not reflect the official policy or position of the United States Department of Defense or the United States Government.

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	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

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