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© 1998 The Journal of Bone and Joint Surgery, Inc. Spontaneous Healing of a Tear of the Anterior Cruciate Ligament. A Report of Two Cases*  , KOBE, JAPANInvestigation performed at the Department of Orthopaedic Surgery, Kobe University School of Medicine, Kobe
The primary healing potential of the anterior cruciate ligament has been reported to be extremely poor in both clinical and experimental studies2,7,9,11,13. This inferior healing capability has led surgeons to reconstruct the anterior cruciate ligament rather than to attempt non-operative treatment involving bracing and muscle-strengthening exercises or to perform a primary suture repair after an acute injury in an athletically active patient12. We report the cases of two patients who had an acute injury of the anterior cruciate ligament that healed spontaneously, as confirmed by arthroscopy and evaluation of stability, after non-operative treatment consisting of early bracing and prolonged restriction of sports activity. Fifty patients who had an acute tear of the anterior cruciate ligament were managed at our institution between May 1991 and April 1993. We recommended delayed reconstruction after diagnostic arthroscopy and rehabilitation for twenty-nine patients and non-operative treatment with modification of activity for twenty-one. At the time of the initial evaluation, both of the patients who are reported on in this paper were advised to have delayed reconstruction.
CASE 1. A twenty-year-old man, who was a college student, sustained an injury to the right knee when he was tackled while playing rugby. He heard a loud pop at the time of the injury and had immediate pain. He withdrew from the game, and ice and a posterior splint were applied immediately. Physical examination performed two days after the injury revealed a grade-1 medial joint opening, indicating a partial tear of the medial collateral ligament. However, the degree of laxity of the anterior cruciate ligament was not clear because it was not possible to achieve complete muscle relaxation. All evaluations of the ligaments were performed on the basis of the International Knee Documentation Committee (IKDC) standard evaluation form1. Examination performed seven days after the injury, with the patient under anesthesia, confirmed the grade-1 medial joint opening; the result of the Lachman test was grade 2 with a soft end point. Measurements with a KT-1000 arthrometer (MedMetric, San Diego, California) revealed a side-to-side difference of eight millimeters with a maximum manual anterior force and the knee in 25 degrees of flexion. A grade of 2 was determined with the pivot-shift test. Arthroscopic evaluation performed after the physical examination showed disruption of the distal end of the anterior cruciate ligament (Figs. 1-A and 1-B). Disrupted fibers, without coverage by synovial tissue, were seen in the anteromedial bundle. Although a portion of the ligament was found to be in continuity within the posterolateral bundle, probing of this section confirmed a complete loss of normal tension. Abundant bleeding from the tibial insertion was noted when the disrupted distal end of the ligament was retracted with a probe. The articular cartilage and menisci were intact. There was no concomitant injury other than that of the medial collateral ligament.
A brace was applied to the knee, and a delayed reconstruction of the anterior cruciate ligament was scheduled. The brace was a double-hinged model without anterior straps. Range-of-motion exercises were recommended and were performed by the patient as tolerated. Full extension was achieved four weeks after the injury. The patient wore the brace full-time during the first eight weeks except while bathing, and he continued to wear it while walking for the next two months. Four months after the injury, the patient returned to our hospital for the scheduled reconstruction procedure. Physical examination with the patient under anesthesia confirmed a full range of motion and some residual medial instability. The Lachman test revealed negligible anterior translation with a firm end point. The anterior drawer test with the knee in 90 degrees of flexion and the pivot-shift test were also negative. Arthroscopy revealed abundant scar tissue at the site where the tear had been confirmed during the initial arthroscopic evaluation. Although the tibial stump of the disrupted ligament was found to have healed to the original attachment, the scar tissue was connected to the anteromedial synovial tissue with a thin pannus-like tissue. The defect was completely filled with scar tissue, but this tissue was still hypervascular (Fig. 1-C). With probing, the tissue was found to have appropriate tension; the tension increased on Lachman testing and anterior drawer testing with the knee in 90 degrees of flexion. No adhesion or other abnormality was found arthroscopically. Measurements with the KT-1000 arthrometer before the arthroscopy showed a side-to-side difference of one millimeter with a maximum manual anterior force and the knee in 25 degrees of flexion. The same value was obtained without use of anesthesia.
Careful, supervised observation was elected, and the planned reconstruction was not performed. Because the granulation tissue was still hypervascular and seemed to have less mechanical strength, we recommended that the patient not participate in athletic activities until six months after the injury. No limitation of the range of motion was detected, and no other symptoms, such as pain, swelling, or giving-way, were noted during the observation period. The patient resumed swimming at six months and running at eight months after the injury, and he resumed playing rugby at ten months. At the time of the two-year follow-up evaluation, he reported that he was continuing to play in college rugby games. Although he had slight medial instability, anterior stability was maintained as indicated by a negative Lachman test and a side-to-side difference of one millimeter as measured with the KT-1000 arthrometer with a maximum manual anterior force and the knee in 25 degrees of flexion. A plain posteroanterior radiograph, made with the patient bearing weight and the knee in 45 degrees of flexion, revealed no sign of degeneration. CASE 2. A seventeen-year-old high-school student sustained an injury to the left knee while he was playing American football. The knee was internally rotated, and valgus stress was applied. The patient heard a pop and immediately felt pain. On the same day, he was brought to the emergency unit of our hospital, and fifteen milliliters of pure, bloody fluid was aspirated from the joint. Physical examination revealed a grade of 3 on Lachman testing with a soft end point; it was not possible to perform the pivot-shift test because of pain. There was a grade-1 medial joint opening with tenderness of the medial femoral condyle. The knee was immobilized in a splint, and ice was applied. Eight days after the injury, an examination performed with the patient under anesthesia confirmed the grade-1 medial joint opening and the grade-3 Lachman sign with a soft end point. A grade-2 pivot-shift sign also was recorded. Stability was not tested with an arthrometer. Arthroscopy showed that the anterior cruciate ligament was torn from the femoral attachment, and palpation with a probe demonstrated complete detachment of the proximal end (Figs. 2-A and 2-B). The mid-portion of the ligament seemed to be intact, and no bleeding or laceration of the remainder of the ligament was noted (Fig. 2-C). The tibial junction of the medial meniscus was partially torn, and bleeding from this area was detected. However, the meniscus was stable, and the remainder of the meniscus was intact. No other associated injuries were found on arthroscopy.
The knee was placed in a custom-made double-hinged brace. The brace had straps that were anterior to the proximal aspect of the tibia in order to prevent excessive anterior translation. Although the patient started to perform range-of-motion exercises two weeks after the arthroscopic evaluation, he continued to wear the brace for five months. Physical examination at three months demonstrated a full range of motion. The Lachman test was performed at four months and was negative with a firm end point. The patient did not participate in any athletic activities for six months after the injury. Six months after the injury, physical examination performed with the patient under anesthesia revealed no side-to-side difference in the results of the Lachman test, the anterior drawer test with the knee in 90 degrees of flexion, or the pivot-shift test. Repeat arthroscopy showed that the detached proximal end of the anterior cruciate ligament was firmly attached to the lateral femoral condyle (the anatomical insertion) (Fig. 2-D). However, a small amount of scar tissue was found to be interposed between the proximal end of the disrupted anterior cruciate ligament and the lateral femoral condyle. The vascularity and tension of the ligament seemed normal on probing. The ligament was taut on both the Lachman test and the anterior drawer test with the knee in 90 degrees of flexion. No adhesion was detected between the anterior and posterior cruciate ligaments.
The ligament was not repaired, and the patient was followed non-operatively, with periodic visits to the hospital. There was no recurrence of the instability. The patient resumed swimming at seven months and running at eight months after the injury. One and one-half years after the injury, he reported full-level participation on his college football team. Three years after the injury, physical examination revealed slight medial instability. The Lachman test was negative with a firm end point, and the pivot shift test also was negative. Testing with the KT-1000 arthrometer showed no side-to-side difference with a maximum manual anterior force and the knee in 25 degrees of flexion. No radiographic sign of degeneration was found.
We have reported two rare cases of documented spontaneous healing of an injured anterior cruciate ligament. It is generally believed that there is almost no healing after a tear of the anterior cruciate ligament. Marshall and Olsson observed complete disappearance of a severed anterior cruciate ligament and marked osteoarthrotic changes in a dog model; those authors concluded that degenerative changes were inevitable in a joint in which the anterior cruciate ligament has been severed. Hefti et al. did not note any healing after complete transection of the anterior cruciate ligament in a rabbit model. Those authors found that partial healing of the injured anterior cruciate ligament might occur if the tear was incomplete but that it would probably be extremely slow. Kleiner et al. reported that healing in a rabbit model was extremely poor even after primary suture of a partially transected anterior cruciate ligament. Noyes et al. stated that non-operative treatment of an acutely injured anterior cruciate ligament does not allow a competitive athlete to return to sports activities requiring changes in direction and pivoting13. In two other studies, primary suture repair did not provide stability to the joint in most patients2,6. On the basis of these studies2,6,13, the conventional treatment of a complete tear of the anterior cruciate ligament has consisted of reconstruction with use of a graft (in patients who have a high level of activity) or of non-operative measures, including rehabilitation and modification of activity, to address the residual instability5,12. There are several possible explanations for the poor healing of anterior cruciate ligaments. The blood supply to the anterior cruciate ligament is minimum; thus, the supply of undifferentiated mesenchymal cells from the surrounding tissue during the initial healing process may be limited. In vitro cultures of cells from the anterior cruciate ligament demonstrated that these cells have a reduced potential for proliferation and migration11. Joint fluid also has been shown to inhibit the proliferation of cells from the anterior cruciate ligament3. The two patients who are reported on in this paper had a distal (Case 1) or a proximal (Case 2) tear; thus, the conditions for healing may have been favorable. Although we did not specifically recommend it, both patients wore the brace for more than four months and waited for more than six months before resuming athletic activities. Perhaps the healed scar tissue was protected from excessive stress until it had remodeled with sufficient strength. Ihara et al. reported successful results after non-operative treatment consisting of early range-of-motion exercises and use of a specially designed brace for the treatment of acute disruption of the anterior cruciate ligament. Those authors emphasized the importance of physiological force applied to the disrupted ligament with motion of the knee while the knee was in the brace. Although the continuity of the ligament was confirmed three months after the injury by repeat arthroscopy, the activity level of the patients and subsequent follow-up data were not reported. Daniel et al., in a prospective outcome study of acute traumatic hemarthrosis, reported that patients who had instability immediately after the injury and did not have operative treatment had a slight decrease in displacement of the joint over time. They speculated that this decrease was secondary to healing of the disrupted anterior cruciate ligament or the secondary stabilizing structures, or both. Buss et al. also reported successful results after non-operative treatment of acute injuries of the anterior cruciate ligament. At an average of forty-six months after the injury, eleven (20 per cent) of fifty-five knees had a decrease of at least one grade on the Lachman test and seven knees (13 per cent) had a difference of less than three millimeters between the injured and the normal knee on testing with maximum manual force and the knee in 30 degrees of flexion. Although the status of the torn ligament was not documented with arthroscopy, possible explanations for the improved grade on Lachman testing include healing of the secondary stabilizing structures, inclusion of patients who had a partial injury of the anterior cruciate ligament, and healing of the completely disrupted anterior cruciate ligament. Although we do not recommend non-operative treatment of every acute tear of the anterior cruciate ligament, protection of the injured knee from undue stress and an adequate rehabilitation program (with prolonged restriction of athletic activity) might favorably alter the course of healing in selected patients in whom the injury is near the origin and insertion of the anterior cruciate ligament. Finally, although both of our patients had a stable knee with excellent function, there may have been some degree of compensation by other ligamentous structures that contributed to these results. It should be remembered that the healing in our patients was noted after a relatively short period of observation; thus, a longer duration of follow-up is needed to confirm the possibility of healing after non-operative treatment.
*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.
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