1 Introduction

Extensor mechanism disruption in a native knee occurs with a frequency of 1.37/100,000 per year for quadricep tendon rupture and 0.68/100,000 per year for patellar tendon ruptures, with risk factors including diabetes mellitus, trauma, and endocrine disorders.^1–3 Additionally, there is a 23.2/100,000 per year incidence of patellar subluxation/dislocation, often occurring in patients with altered anatomy or ligamentous laxity.⁴ These injuries are often amenable to reconstruction, with great success often seen in patients with early reoperation and rehabilitation.² Despite high recovery rates, these patients often necessitate total knee arthroplasty (TKA), either from residual limited stability/mobility from their injury or the progression of degenerative joint disease.^2,3

A rarer, yet more serious complication, is extensor mechanism failure following TKA, with reported incidences of 0.1–2.5 % in the literature.⁵ This complication poses a serious risk to patients, often necessitating the need for reoperation.⁵ However, the results of primary repair and reconstruction are fraught with both relatively high failure and complication rates.⁶ Brown et al. found a 38 % failure rate following extensor mechanism allograft reconstruction after TKA, including high incidences of revisions and deep infections.⁶ However, more recent results with mesh reconstruction have shown lower failure rates.⁷

Despite prior extensor mechanism problems being relatively common in the joint replacement population, there is minimal literature describing the impact of these prior diseases on the results of subsequent total knee arthroplasty. The purpose of this study was to evaluate the rates of post-operative complications, including extensor mechanism disruption, following TKA in patients with a history of prior extensor mechanism dysfunction (EMD).

2 Methods

This was an IRB approved retrospective cohort study. Inclusion criteria included patients who underwent a primary TKA following EMD between April 2007 and April 2023. EMD included patients with a history of patellar fracture, patellar tendon rupture, patellar realignment surgery, previous patellar dislocation, or a chronic lateral tracking patella impacting extensor mechanism function.

Variables of interest included baseline demographic and patient characteristics (age, gender, race/ethnicity, tobacco use, hypertension, diabetic mellitus, and immunocompromised status), EMD classification and treatment method, and post-operative complications. The primary outcome of this study was extensor mechanism disruption following TKA. Secondary post-operative outcomes included superficial surgical site infection (defined as superficial tissue infection treated with oral antibiotics), deep surgical site infection (defined as return to the operating room for irrigation and debridement), dislocation, aseptic loosening, revision surgery, wound dehiscence, and post-operative stiffness requiring manipulation under anesthesia.

3 Results

A total of 61-knees, comprised of 53-patients, met the study criteria during the enrollment period (April 2007–April 2023) with an average follow up of 48.0 months (Std deviation, 44.1). These patients underwent a primary TKA and had a history of EMD in the ipsilateral knee. The most common type of EMD witnessed was chronic lateral patellar tracking (59.0 %), followed by patellar fracture (21.3 %), patellar tendon disruption (6.6 %), patellar dislocation (6.6 %), and other (6.6 %). “Other” injuries included two previous patellar realignment surgeries, one tibial tuberosity osteotomy, and one absent patella. Most of these injuries were treated nonoperatively (77.05 %) (Table 1). While only fourteen patients had their EMD operatively treated, an additional thirteen patients had other procedures on their ipsilateral knee not related to the extensor mechanism.

The average patient age was 62.1 years-old (range, 39–92 years) and 72.1 % of the patients were women. Common comorbidities included hypertension (68.9 %) and diabetes (18.0 %). Most of the patients denied ever having used tobacco (65.6 %), followed by former (24.6 %) and current (9.8 %) tobacco use (Table 1).

Complications were witnessed in 15 patients (15 knees), leading to an overall complication rate of 24.6 %. There was one extensor mechanism disruption in the form of a partial quadriceps tendon rupture requiring repair. There was one patellar dislocation, requiring reoperation for lateral release and medial plication. Other complications included five superficial surgical site infections successfully treated non-operatively, along with four deep surgical site infections requiring reoperation. There was a total of nine reoperations (14.8 %), four of which were revisions. Two revisions were performed for infection, one for TKA failure due to instability/soft tissue laxity, and one for aseptic loosening. The other five reoperations were performed for two infections, one traumatic wound dehiscence, and the previously mentioned patellar dislocation and quadriceps tendon repair. Finally, four patients experienced post-operative stiffness requiring manipulation under anesthesia (Table 2).

Of the patients who experienced complications, the most common prior EMD was chronic lateral patellar tracking (80.0 %), followed by patellar fracture (13.3 %), and tibial tuberosity osteotomy (6.7 %). Over half (53.3 %) of the patients who experienced a complication had undergone a previous surgery on their ipsilateral knee prior to the TKA (Table 3).

4 Discussion

As the rate of TKAs continues to crescendo with the aging population, so will the rate of patients with prior EMD necessitating this operation.⁸ While the complication profile following TKA has been previously well established, there is a scarcity of literature describing the complication rates following TKA in patients with prior EMD.^9–12

In this study, we found a high complication rate of 24.6 % in patients with a history of EMD who underwent primary TKA, especially regarding infection. Over half of these patients who developed a complication had undergone a previous surgery on their ipsilateral knee prior to the TKA. Only three out of those eight operations, however, were for the prior EMD with the other five being unrelated procedures. This aligns with previous studies that have demonstrated increased complication rates following TKA in patients with prior knee surgery.^13–16 These studies have reported increased incidences of infection, reoperation, and revisions in this subset of patients.¹⁶ Thus, it may be advisable to be as conservative as possible with arthroscopy and other procedures if a TKA is anticipated down the road.¹⁶

Of note, there was one case of extensor mechanism disruption observed in this study in the form of partial quadriceps tendon rupture requiring repair. There was also one patellar related complication of dislocation, which required reoperation. Extensor mechanism failure following TKA is already a rare complication, with rates of 0.1–2.5 % stated in the literature.^5,17,18 This study found an incidence of 1.6 %, suggesting that prior extensor mechanism injury does not significantly increase a patient's risk for extensor mechanism failure following TKA, though it does appear to increase overall complication rates.

The retrospective design of this study inherently presents numerous limitations, given the potential for recall bias. Additionally, while there was consistent patient follow-up in this cohort, we acknowledge that patients may have presented to outside institutions with complications. Finally, the small cohort size also presents a limitation. To our knowledge, however, this is the largest study to date evaluating the impact of prior extensor mechanism injury on TKA complications. Future large-scale studies are warranted to further evaluate extensor mechanism function and overall complication rates following TKA in patients with previous EMD.

5 Conclusion

This study found a high rate of complications, particularly infection, in patients with prior extensor mechanism injury who underwent primary total knee arthroplasty. Notably, there was one case of partial quadriceps tendon rupture observed post-operatively requiring repair.

CRediT authorship contribution statement

Whisper Grayson: Methodology, Investigation, Data curation, Writing – original draft. Nathaniel Baek: Data curation, Writing – review & editing. William Hopkinson: Supervision, Writing – review & editing. Daniel Schmitt: Supervision, Writing – review & editing. Nicholas M. Brown: Conceptualization, Supervision, Writing – review & editing.

Consent

Institutional Review Board approval was submitted and received for this study, and the manuscript is not submitted elsewhere for publication consideration.

Ethical review committee statement

The study has been performed in accordance with the ethical standards in the 1964 Declaration of Helsinki and has been carried out in accordance with relevant regulations of the US Health Insurance Portability and Accountability Act (HIPAA).

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.