The most important findings of the present study were that the result of direct repair after extensor mechanism disruption showed poor outcomes at long-term follow-up. The postoperative patients had low range of motion, accompanied by severe extension lag, and the incidence of postoperative complications was high. Previous studies were limited by the relatively small case number as well as only investigating a certain site of extensor mechanism disruption. We provided a more complete and more comprehensive case series. Second, our study showed a low success rate of direct repair and low patient satisfaction compared with other studies. Other treatments shown better postoperative results. We suggest that direct repair should not be the first choice for the treatment of extensor mechanism disruption.
Although extensor mechanism disruption was a rare complication following total knee arthroplasty with incidence ranging from 0.1–3%1,2. Once it happened, it would have a devastating impact on the patients' daily life after operation, and often resulted in frequent falls, difficulty in walking, and pain12,13. The treatment of extensor mechanism disruption after TKA had remained a challenge for decades14, the ideal method of treatment remained unclear. There have been few recent reports of direct repair after extensor mechanism disruption in arthroplasty patients, except for published in 200515 and 201816. Our current case series provides an updated report about this challenging complication, including quadriceps tendon rupture、patellar tendon rupture and patellar fracture.
Tracing back to the source, we found two reports about direct repair of extensor mechanism disruption after TKA in earlier years. In 1987, Lynch et al. reported extensor mechanism complications in 281 TKA17. Among these complications were eight extensor mechanism disruptions. Of the four patellar tendon ruptures were direct repaired, one re-ruptured at four weeks after the operation, two had residual extensor lags of 18° and 22°, and 1 became infected. Of the three quadriceps tendon ruptures were repaired primarily, one re-ruptured at six weeks after the operation, two with residual extensors lags of 12° and 19°, and knee flexion of only 70°. One patella fracture was repaired went on to develop avascular necrosis requiring patellectomy with subsequent post-operative infection and ultimately a knee arthrodesis. In the report of Lynch et al, the failure rate of directly repair of extensor mechanism disruption is 50%, the average residual extensor lag in successful cases was 17.8 °, and knee flexion of 70°. In 1989, Rand et al. reported extensor mechanism complications in 16 TKA, all of which were repaired directly except 3 cases10. Of the nine patella tendon ruptures were treated with direct repair, all nine failed with six re-rupturing after the operation and three became infected. In the report of Rand et al, the failure rate of directly repair of extensor mechanism disruption is 85%, the average residual extensors lag in successful cases was 1 °, and average knee flexion of 81°. While the results from the Lynch et al and the Rand et al. studies showed less extension lag compared to our current study, only slightly floating compared to ROM, but the incidence of postoperative complications was much higher than ours. We studied more patients (31 vs. 8 and 13) which may account for this difference.
Dobbs et al15 and Courtney et al16 are two rare reports on direct repair after extensor mechanism disruption in recent years. In the report of Dobbs15, 26 patients with rupture of quadriceps tendon underwent direct repair. The results of the report are divided into complete rupture and partial rupture of the quadriceps tendon parts. In 10 patients of complete rupture, the rate of postoperative complications was 60%, four of the ten patients had a re-rupture of the quadriceps tendon after operative repair, two patients had a deep periprosthetic infection develop, The active range of motion before a complete tear of the quadriceps tendon averaged 2° (range, 0° to 8°) of extension and 106° (range, 95° to 135°) of flexion. At the time of the last follow-up, the active range of motion averaged 3° (range, 0° to 10°) of extension and 101° (range, 60° to 125°) of flexion. In 16 patients of partial rupture, the rate of postoperative complications was 31༅, five of the sixteen patients had a complication including knee instability, re-rupture, intraoperative laceration of the popliteal artery, intraoperative fracture of the femoral condyle, or deep periprosthetic infection. The active range of motion in the sixteen patients before the partial tear of the quadriceps tendon averaged 4° (range, 0° to 20°) of extension and 110° (range, 90° to 130°) of flexion. The active range of motion after the operative repair averaged 7° (range,0° to 40°) of extension and 104° (range, 90° to 130°) of flexion. All patients had a mean Knee Society knee score of 74 points and a mean Knee Society function score of 44 points. In the report of Courtney et al16, 58 patients with extensor mechanism disruption underwent direct repair. We analyzed the data of this document about direct repair and come to the conclusion that the reoperation rate was 30༅,the mean postoperative extensor lag was 4.15°༌and the mean postoperative flexion was 104.9°༌the mean postoperative KSS was 121.6. Although the postoperative range of motion of the patients in this report was high, there was no significant improvement compared with that before operation, and the incidence of complications was still very high.
In our research, the failure rate of direct repair was 19%, the average residual extensors lag in cases was 20.2 °, and average knee flexion of 71.6°, the WOMAC and HSS averaged 64 and 72 points. Combined with the above four reports, the postoperative range of motion decreased or had hardly changed compared with that before operation, and the motion is limited. What's more serious was that there was severe knee extension lag, it will seriously affect the knee joint function. High incidence of postoperative complications also greatly increased the failure rate of surgery, and the postoperative scores showed poor recovery. It is far from enough to meet the patients' normal daily life after operation. Judging from these results, the result of direct repair is not satisfactory.
In addition to direct repair, there were other multiple surgical options for extensor mechanism disruption, including reconstruction with allograft, autograft and synthetic material18. There was no consensus in the report as to the type of extensor mechanism reconstruction that yields the best results. At present, more and more evidence proved that the therapeutic effect of direct repair was unsatisfactory, which made us have to compare with the results of other treatments, in order to judge whether there was a better treatment.
Allograft augmentation had been considered the gold standard with multiple reports1,19,20. In the report of Wise et al21, Sixteen patients with 17 reconstructions (10 patellar tendons, 7 quadriceps tendons) were treated with achilles tendon allograft. All patients underwent evaluation at an average of 45.7 months. After reconstruction, the average extensor lag was 6.6° and average knee flexion was 105.1°,the extensor lag(6.6° vs 20.2° ) was significantly lower and the knee flexion(105.1° vs 71.6° ) was significantly higher. In addition to Allograft, we found an up-to-date literature on synthetic material. Besides, monofilament polypropylene mesh has emerged as the preferred treatment11. In the report of Buller et al11, 30 patients were treated with Marlex Mesh. The failure rate of the operation was 27%. Of the successful extensor mechanism reconstructions, extensor lag improved a mean of 34°, with the average final lag measuring 9°± 8°, the average final active range of motion was 9° to 107 ± 15 degrees of flexion. The extensor lag (9°± 8° vs 20.2°) was significantly lower and the knee flexion (107 ± 15° vs 71.6°) was significantly higher than ours. Similar results were found in comparison with the literature on autograft22, where postoperative range of motion and the extensor lag were better than direct repair.
There were several limitations to this study, including its retrospective design. A limitation of our study was the small number of cases due to the low incidence of extensor mechanism disruption. We present the largest series to our knowledge, including quadriceps tendon rupture、patellar tendon rupture and patellar fracture. The operative reports were also not consistent in commenting on the quality of the tissues, the characteristics of the rupture, or the patellar fracture pattern.
After comparison with these reports, no matter whether we choose allograft, autograft or synthetic material to reconstruct extensor mechanism, the result of direct repair is not as ideal as that of these treatments. And direct repair had the severe extensor lag after operation, which will have a great impact on the postoperative function of the patients. After the failure of direct repair, these reconstruction methods can also be used as remedial measures. Just like the five patients who failed after operation in our cases, three of them received semitendinosus reconstruction and Marlex mesh reconstruction respectively, and all the patients recovered well after operation.