At 1 year postoperatively, the patient reported significant functional improvement and stability of his left knee. He reported that he had ridden his bike over 4,000 km throughout the summer. On examination, he had no circumference deficit of his quadriceps muscles when measured at 3, 5, and 10 cm proximal to the superior patella border. The Banff Patellar Instability Instrument (BPII) score, a quality-of-life measure for patellofemoral instability, was recorded as 76.6/100. The surgeon's global rating score for 1-year outcomes was excellent.
At 3 years postoperatively, the patient reported that he was very satisfied with the outcome of his procedure, rating it as 9/10 on a 10-cm visual analog score scale. The patient was able to bicycle almost 7,000 km annually and reported being able to ski with no symptoms in his knee. The BPII score was assessed as 98.9/100. Knee range of motion was measured as R7-133° on the right compared with R5-124° on the left. Manual muscle testing strength was assessed as 5/5 bilaterally for both hip adduction and abduction, with 4/5 hip internal rotation and 5/5 hip external rotation. This was compared with full 5/5 strength of the contralateral nonoperative limb. Knee extension manual muscle testing was 4/5 on the left compared with 5/5 on the right. The patient reported that he was able to perform a straight leg raise on either leg while wearing his skis. Thigh circumference measured at 3 and 10 cm proximal to the superior border of the patella was 40.4 and 44.2 cm, respectively, on the left, compared with 43.5 and 48.3 cm, respectively, on the right leg. The patient has had no further episodes of subluxation, instability, locking, or catching in the operative knee.
Gait demonstrated equal stride length and good bilateral control throughout the swing and stance phases. Functionally, the patient was able to perform full double-leg squats with excellent control, as well as single-leg squats with good control and depth on his operative left leg, compared with excellent control and depth on his right. Additionally, left single-leg balance assessed on a Bosu ball was within 3 seconds of the right limb. Results of the single-leg hop for distance demonstrated a distance of 1.19 m on his nonoperative right leg compared with 0.68 m on his left. His single-leg triple hop for distance and crossover hop for distance, however, were both within 90% of the contralateral nonoperative right leg.
This case describes an unusual complication after patellectomy of a subluxating extensor mechanism that was stabilized by performing an MQTFL reconstruction. This was completed in combination with a tibial tubercle medializing and distalizing osteotomy, which improved the tension in the extensor mechanism to optimize strength and function.
Patellectomy is considered a salvage procedure, and postoperative complications are common, including osteoarthritic degeneration, extensor tendon rupture, extensor tendon dislocation, quadriceps tendon ossification, quadriceps weakness, pain, and dysfunction.4–8 In 2014, Cavaignac et al5 published a systematic review on the results of patellectomy in patients without a prior total knee arthroplasty. They analyzed 31 articles describing 1,416 knees with a mean follow-up of 7 years and reported a 20.3% complication rate. There were only four reported cases involving a dislocation of the extensor mechanism. This represents merely 1.8% of all the complications recorded and 0.36% of the patellectomies performed. Ackroyd et al9 reported on three cases of anterior knee pain and extensor mechanism instability after patellectomy. Of these seven cases of dislocating extensor mechanism reported in the literature, five were managed operatively with either a tubercle transfer (n = 2) or a patellofemoral arthroplasty with lateral release and medial reefing (n = 3), with good results.
In addition to instability of the extensor mechanism, weakness of knee extension is also a reported issue after patellectomy. Watkins et al10 performed Cybex testing after patellectomy and demonstrated that quadriceps strength was significantly impaired postoperatively. The patient group in this study was relatively early postoperative, at 14 to 42 months; however, these results are similar to those reported by Lennox et al11 for 69 patients and 83 knees assessed 12 to 48 years after patellectomy. Hill et al12 reported on the correlation of knee extensor strength and outcome after patellectomy. These authors determined that patients with a quadriceps strength loss of 45% or less had superior postoperative outcomes.
In this case report, the patient initially described a significant dysfunction from the instability of the knee extensor mechanism as his main concern. Although reduced function and strength of the injured knee were noted as an issue after the patellectomy, the patient reported moderately good function until he developed the extensor mechanism instability. The surgical intervention combined an MQTFL reconstruction with a tibial tubercle distalization to address both of these patient concerns. After the tubercle osteotomy and lateral release, the extensor mechanism continued to be readily dislocatable with only slight lateral pressure. The realignment procedure served to improve the biomechanics about the knee, especially regarding tensioning the quadriceps; however, the MQTFL reconstruction was required to provide stability to lateral translation of the extensor mechanism. Postoperative rehabilitation was phase-based to encourage functional performance gains, with a particular focus on strengthening of the core, hip, and thigh musculature. Through surgical stabilization and retensioning of the extensor mechanism, the patient was able to achieve significantly improved function and participation in demanding recreational activities.
Extensor tendon instability is a rare complication after patellectomy that can cause significant pain and dysfunction. Successful stabilization of the quadriceps mechanism through an MQTFL reconstruction as described in this case report can provide excellent patient satisfaction and functional results.
The authors thank Allison Tucker, MD, FRCSC, for contributing to the manuscript.
References printed in bold type are those published within the past 5 years.
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Copyright © 2017 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Orthopaedic Surgeons
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