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A retrospective review of delayed knee mobilization following extensor mechanism repair
*Corresponding author: Juan D. Bernate, MD, Department of Orthopedic Surgery, Geisinger Medical Center, Danville, Pennsylvania, United States. jbernate@geisinger.edu
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Received: ,
Accepted: ,
How to cite this article: Bernate JD, Dahodwala TM, Mahmoud AN, Horwitz DS. A retrospective review of delayed knee mobilization following extensor mechanism repair. J Musculoskelet Surg Res. doi: 10.25259/JMSR_491_2025
Abstract
Objectives:
Traumatic extensor mechanism (EM) rupture of the knee is a debilitating injury with considerable post-operative morbidity. While surgical repair is standard, rehabilitation protocols vary. This study aimed to evaluate clinical outcomes of patients managed with delayed knee flexion, initiated at least 6 weeks after EM repair.
Methods:
We retrospectively reviewed patients who underwent acute surgical repair of the EM at a level 1 trauma center over a 10-year period. Adults with patellar fractures, quadriceps, or patellar tendon ruptures were included. All were allowed weight-bearing as tolerated but restricted from active or passive knee flexion for 6 weeks. Outcomes included the final range of motion, return to pre-injury activity, and post-operative complications.
Results:
Of 149 patients included, the mean body mass index (BMI) was 31.5. Patellar fractures comprised 67% of cases, followed by quadriceps tendon ruptures (31.8%) and patellar tendon ruptures (6.8%). Most had no wound complications (94.7%) or revision surgeries (93.96%). Patients with tendon ruptures were older (59.0 vs. 54.5 years, P = 0.04) and had a higher BMI (36.0 vs. 27.9, P < 0.0001) than those with fractures. Median final flexion was 120° for fractures and 110° for tendon ruptures (P = 0.93). Manipulation under anesthesia was rare (4.1% vs. 3.9%), and fixation loss occurred in 5.3% of patients.
Conclusion:
Delayed flexion beginning at 6 weeks after EM repair is associated with a favorable range of motion and low complication rates. These findings suggest that delayed mobilization does not compromise outcomes and is a safe alternative to early motion protocols.
Keywords
Knee injuries
Patellar fractures
Range of motion
Rehabilitation
Tendon injuries
INTRODUCTION
The extensor mechanism (EM) of the knee is comprised of three parts: The quadriceps tendon, the patella, and the patellar tendon. The rupture of this apparatus can be divided into a bony, when a patellar fracture is present, or soft tissue, when there is a quadriceps or patellar tendon rupture. The incidence of EM injuries (EMIs) is 3.47/100,000, with patellar fractures accounting for the majority (77.5%), followed by patellar tendon ruptures (13.5%) and quadriceps tendon ruptures (9%).[1,2] EMIs often occur following direct trauma, such as falls or motor vehicle accidents, or indirect trauma caused by forceful eccentric or concentric quadriceps contraction during knee flexion. The latter is commonly associated with predisposing factors, including diabetes mellitus, gout, repetitive microtrauma, and endocrine disorders.[2-5] Despite its low incidence, this injury is significantly debilitating due to its impact on the knee joint. Inadequately repaired or improperly rehabilitated EMIs may result in stiffness, arthritis, and loss of extension.[6]
Post-operative joint mobilization is critical for a successful recovery after EMI repair. Surgeons in the past have advocated early post-operative mobilization in an attempt to reduce the risk of knee stiffness, arthrofibrosis, and muscle atrophy.[7-9] However, a systematic review published by Serino et al.[10] found a significantly higher adverse event rate (P = 0.02) associated with early post-operative mobilization (within 6 weeks after surgery).
Given the evidence on early mobilization and its association with higher complication rates, it remains unclear whether prolonged immobilization provides a protective benefit or introduces its own set of complications. This study aimed to assess the outcomes of delayed active flexion or any range of motion for at least 6 weeks following EM repair.
MATERIALS AND METHODS
Study design and patients
We conducted a retrospective review of patients who underwent EM repair at our hospital between January 2011 and January 2021. All consecutive patients aged ≥18 years treated by four senior surgeons were included. Patients with pathological fractures or early post-operative mobilization were excluded.
Of 176 eligible patients, 17 were lost to follow-up and 10 did not meet the inclusion criteria, resulting in a final cohort of 149 patients. Patients were categorized by injury type: Bony (transverse, comminuted, or pole patella fractures) and ligamentous (quadriceps or patellar tendon ruptures). All underwent operative treatment and followed the same postoperative protocol. Weight-bearing was allowed as tolerated, but active and passive knee flexion was restricted for at least 6 weeks unless limited by other injuries.
Clinical records were reviewed to collect data on demographics, injury mechanism, surgical timing, range of motion, strength, and complications. All surgeries were performed within 2 weeks of injury.
Surgical technique and post-operative management
All patients underwent surgical treatment in a supine position with complete paralysis, performed by four senior surgeons using a midline approach for open reduction and internal fixation (ORIF). Patellar fractures were reduced with clamps, and implant selection was based on the surgeon’s preference, including stainless steel Kirschner wires, tension band wiring, screws, plates, FiberWire, and Nitinol staples. Initially, stainless steel tension bands were preferred, but surgeons later transitioned to FiberWire.
A Krackow suturing technique was used for tendon repairs, with Fiberwire or Ticron, and occasionally FiberTape. A minimum of two sutures were utilized and passed through the patella through drill holes. After repair, knee stability was confirmed by passive flexion to 60°. Once the incision was closed, the leg was immobilized in a hinged knee brace locked in full extension.
Postoperatively, wounds were checked, and sutures were removed at 2 weeks. Patients were advised to elevate their legs for the first 7 days. The brace remained locked for 6 weeks, removed only for hygiene and wound care. Patients were allowed to bear full weight-bearing unless restricted by other injuries. No active or passive knee flexion was permitted for the first 6 weeks.
At 6 weeks, if no complications were present, patients began active flexion and strict passive extension of the knee under the guidance of a physical therapist. In addition, patients began with brace quad sets and straight leg raises at 6 weeks. The hinged knee brace remained locked in full extension during ambulation and was discontinued at 12 weeks postoperatively, after which the patients began active extension and strengthening protocols.
All patients were evaluated at 2 and 6 weeks and then at 3 and 6 months. If any complications were noted or the patient had not achieved the desired motion by 6 months, they were reevaluated at 12 months. Post-operative radiographs were obtained at 6 weeks, 3 months, and 6 months for the bony fractures, with no routine imaging for the tendon ruptures.
Outcomes and statistical analysis
The primary outcome was active knee range of motion, measured with a standard goniometer at the 6-month post-operative visit. This point was applied uniformly to all patients and represented the final functional assessment after completion of the rehabilitation protocol. The secondary outcomes included the incidence of postoperative complications, such as surgical wound infections, wound dehiscence, implant failure, loss of reduction, and reoperation rates. Loss-of-reduction or implant failure cases were further analyzed to determine their causes.
Descriptive statistics were used to describe patient characteristics and the type of injury. Categorical variables were reported as frequencies and percentages, while continuous variables were summarized using means and standard deviations. For continuous variables that did not follow normal distribution, medians and interquartile ranges were reported. Comparisons between injury types were conducted using the Chi-square or Fisher’s exact test for categorical variables. In addition, a Mann–Whitney test or an independent two-sample t-test was used to compare the differences in age, body mass index (BMI), extensor lag, and final flexion range angle between the fracture and the tendon rupture groups.
RESULTS
Patient demographics
A total of 176 patients with EM rupture were treated during the 10-year timeline. Of these, 118 cases involved bony injuries, and 58 involved soft tissue injuries. Among the 118 patellar fractures, 48 were transverse fractures, 53 were comminuted fractures, and 17 were pole fractures. The soft tissue injuries included 47 quadriceps ruptures and 11 patellar tendon ruptures. In addition, eight open patellar fractures were included in the study. Seventeen patients were lost to follow-up, and 10 did not meet the inclusion criteria; therefore, the final analysis included 149 patients.
The mean age of all the patients was 57 years (range: 16–84 years). The sex distribution included 96 males and 53 females. Among the 98 patients with patellar fractures, there were 50 males (51%) and 48 females (49%). In the 51 tendon rupture cases, 46 patients (91%) were males and only 5 (9%) were females [Table 1].
| Variable | All (n=149) |
|---|---|
| Age, median (IQR) | 57.0 (43.0, 65.0) |
| BMI, mean (SD) | 31.1 (7.4) |
| Extensor lag | |
| Mean (SD) | 0.76 (3.71) |
| Median (IQR) | 0 (0,0) |
| Missing | 2 |
| Final flexion lag, median (IQR) | 115.0 (110.0, 120.0) |
| Missing | 4 |
| Fracture type, n(%) | |
| Transverse patella fractures | 38 (25.5) |
| Comminuted patella fractures | 43 (28.9) |
| Pole fractures | 17 (11.4) |
| Quadriceps tendon rupture | 42 (28.2) |
| Patella tendon rupture | 9 (6.0) |
| Wound complications, n(%) | |
| Yes | 7 (4.7) |
| No | 142 (95.3) |
| Reoperation/need for surgery, n (%) | |
| Yes | 27 (18.1) |
| No | 122 (81.9) |
BMI: Body mass index, SD: Standard deviation, IQR: Interquartile range
The mean BMI for the entire study population was 31.1 kg/m2. Patients with patellar fractures had a mean BMI of 27.9 kg/m2, while those with tendon ruptures had a significantly higher mean BMI of 36.0 kg/m2 (P < 0.0001).
Injury characteristics
In the study population, patellar fractures were classified into transverse (n = 38), comminuted (n = 43), and patellar pole (n = 17) fractures. These fractures were categorized using the AO classification, with 81 of the 98 patellar fractures classified as type C fractures and 17 as type A fractures. More specifically, 38 patients (38.7%) had transverse fractures (C1 fractures), 43 (43.8%) had comminuted fractures (C2 and C3 fractures), and 17 (17.3%) had type A1 fractures.
The soft tissue injuries were divided into quadriceps ruptures (n = 42) and patellar tendon ruptures (n = 9).
Surgical treatment
All bony fractures underwent ORIF with either Kirschner wires, screws, stainless steel wire, patella plates, or nitinol staples.
Most of the tendon repairs were carried out using transosseous suture techniques with three drill holes in the patella and two strands of #5 FiberWire. Modified Kessler and Krackow suturing techniques were utilized for fixation to the quadriceps or patellar tendons, depending on the type of injury.
Post-operative rehabilitation
Of the 149 patients, 141 were allowed full weight-bearing immediately, while eight patients (5%) had weight-bearing delayed for 6 weeks due to concomitant fractures in other areas, such as the acetabulum or proximal tibia, necessitating a modified rehabilitation protocol. However, all patients were placed in a hinged knee brace locked in full extension for the first 6 weeks.
Clinical outcomes
Six months after surgery, rehabilitation outcomes were assessed by measuring the range of motion and extensor lag, if present. The final average flexion achieved for all the patients was 115° (interquartile range: 110°–120°). Patellar fractures had an average final flexion of 120° while tendon ruptures (quadriceps and patellar tendon injuries) averaged 110°. Transverse and comminuted fractures had a median final flexion of 115° and 120°, respectively. A total of eight patients developed extensor lag, including three patients with patellar fractures (range: 3°–20°) and five patients with quadriceps ruptures (range: 5°–30°). Thirteen patients (13.3%) with patellar fractures underwent implant removal due to painful hardware. Table 2 summarizes the comparison between outcomes in patellar fractures and tendon ruptures.
| Variable | Patella fractures (Transverse, Comminuted, Pole) n=98 | Tendon ruptures (Quadriceps+Patella) n=51 | P-value |
|---|---|---|---|
| Age, median (IQR) | 54.5 (35.0, 64.0) | 59.0 (48.0, 66.0) | 0.04a |
| BMI, median (IQR) | 27.9 (24.4, 32.1) | 36.0 (32.0, 39.0) | <0.0001a |
| Extensor lag, | |||
| Mean (SD) | 0.42 (2.55) | 1.4 (5.3) | 0.15a |
| Median (IQR) | 0 (0, 0) | 0 (0, 0) | |
| Missing | 1 | 1 | |
| Final flexion lag, median (IQR) | 120.0 (110.0, 120.0) | 110.0 (110.0, 120.0) | 0.93a |
| Missing | 3 | 1 | |
| Wound complications, n(%) | |||
| Yes | 6 (6.1) | 1 (2.0) | 0.42b |
| No | 92 (93.9) | 50 (98.0) | |
| Reoperation/need for surgery, n(%) | |||
| Yes | 22 (22.5) | 5 (9.8) | 0.06c |
| No | 76 (77.6) | 46 (90.2) |
SD: Standard deviation, IQR: Interquartile range. P-values < 0.05 were considered statistically significant. aWilcoxon (Mann–Whitney test); bFisher’s Exact test; cChi-square test
Complications
Infections and wound complications
In our series, six patients (6.1%) with patellar fractures (three transverse and three comminuted fractures) and one (2%) quadriceps tendon rupture developed post-operative infections.
Of the six patients with infected patellar fractures, four had open fractures, which placed them at a higher risk of infection. All infected patients were treated with antibiotics and multiple debridement procedures and, if necessary, implant removal, with one of them resulting in an amputation above the knee. The remaining patients healed with good final knee flexion.
Among the tendon rupture cases, the only infected patient was a morbidly obese individual (BMI = 47.6) with severe diabetes mellitus and peripheral neuropathy. This patient underwent one surgical debridement and a quadriceps tendon re-repair 1 month after the initial surgery.
Fixation failure
Implant failure requiring revision surgery occurred in five patients (5.1%) with patellar fractures, including two transverse fractures, two comminuted fractures, and one pole fracture, which can be shown summarized in Table 3. Post-operative management was individualized; however, the rehabilitation timeline was typically restarted to ensure protection of the revised repair. Two patients with open fractures developed post-operative infections, which ultimately resulted in fixation failure and the need for revision surgery.
Among the tendon rupture cases, three patients with quadriceps tendon ruptures experienced fixation failure. In two of these cases, sudden traumatic knee flexion at 4 and 10 weeks led to fixation loss requiring revision surgery. The third patient developed a post-operative infection, necessitating surgical debridement and fixation revision. A summary of these findings is provided in Table 3.
| Variable | Transverse patella fracture | Comminuted patella fracture | Pole patella fracture | Quadriceps rupture | Patella tendon rupture | P-value |
|---|---|---|---|---|---|---|
| Infection, n(%) | 3 (7.9) | 3 (7.0) | 0 (0) | 1 (2.4) | 0 (0) | 0.71a |
| Failure, n(%) | 2 (5.3) | 2 (4.7) | 1 (5.9) | 3 (7.1) | 0 (0) | 0.97a |
| Manipulation, n(%) | 1 (2.6) | 3 (7.0) | 0 (0) | 2 (4.8) | 0 (0) | 0.86a |
| Implant removal, n(%) | 7 (18.4) | 5 (11.6) | 1 (5.9) | 0 (0) | 0 (0) | 0.03a |
Manipulation under anesthesia (MUA)
A total of 4 patients (4.1%) with patellar fractures and 2 patients (3.9%) with tendon ruptures required MUA. Manipulation was warranted in those cases that had not achieved a minimum of 90° of flexion by 12 weeks. Three of the four patellar fractures were comminuted fractures, while both patients with tendon rupture requiring MUA had quadriceps tendon ruptures. The mean range before MUA on these patients was 70° (range: 65–80°) and the mean final flexion after manipulation was 116° (range: 110–130°).
Extensor lag
At the 6-month follow-up, three patients with patellar fractures did not achieve full knee extension. This included two patients with comminuted fractures, presenting with 3° and 15° of lag, and one patient with an inferior patellar pole fracture, who had a 20° extensor lag. No patients with transverse patellar fractures experienced extensor lag.
None of the patients with patellar tendon ruptures had an extensor lag. However, five patients with quadriceps tendon rupture had an incomplete extension, with extensor lags of 5°, 5°, 10°, 20°, and 30°.
DISCUSSION
Recently, the recommended treatment for EM repair has involved fracture fixation or tendon repair, followed by 6 weeks of immobilization. While concerns about muscle weakness, limited flexion, and persistent pain have led to interest in early mobilization strategies,[7-9,11] recent studies have highlighted the increased risk of complications associated with early motion.[10] It has been theorized that early mobilization enhances collagen organization, increases filament density, and improves the breaking strength of the EM.[12-15] However, these potential benefits must be weighed against the higher incidence of fixation failure, extensor lag, and the need for revision surgery. In response to these risks, augmentation techniques such as cerclage wires,[8,16] Dacron grafts,[17,18] Mersilene tapes,[19,20] and muscle grafts[21,22] have been introduced to improve stability and reduce failure rates. However, these methods can add surgical complexity, increase implant costs, and prolong operative time. Despite the growing debate, comparative studies directly evaluating early versus delayed mobilization remain limited, and definitive evidence favoring one approach over the other is still lacking.
Enad and Loomis[23] reported no significant clinical or functional differences between patients treated with early or delayed mobilization in a retrospective chart review. Similarly, Rougraff et al.[24] found that 67% of patients undergoing early mobilization and 19% of those mobilized after 3–6 weeks showed an extensor lag, though the difference was not clinically significant. However, recent higher-level evidence challenges the idea of early mobilization. Serino et al.[10] conducted a meta-analysis comparing adverse events and post-operative mobilization, concluding that early mobilization is associated with a significantly higher rate of complications and overall adverse events compared to a minimum of 6 weeks of fixed immobilization (0.21 vs. 0.04, P < 0.001). Their findings suggest that early mobilization imposes a greater financial burden and contributes to a lower quality of life. West et al.,[7] in a retrospective review of patients with early motion after quadriceps and patellar tendon repairs, reported that all 50 patients achieved a full range of motion (defined as active knee flexion equal to or within 10° of their uninjured knees) after 12 weeks, with no post-operative complications. Their technique involved the use of a relaxing Ethibond suture placed at 30° of flexion alongside a drill-hole repair. While their study demonstrated that early motion is successful with this specific surgical technique, the broader evidence base, particularly Serino et al.’s[10] meta-analysis, suggests that early mobilization may come at the cost of increased complications.
In our cohort, patients were allowed immediate weight-bearing in full extension with active flexion and passive extension initiated at 6 weeks and no passive flexion or active extension before 12 weeks. This approach resulted in favorable functional outcomes, with a median final flexion of 115° across all EM ruptures. Only eight patients (5%) experienced extensor lag at 6 months.
A notable finding in our study was the significant difference in BMI between patients with tendon ruptures and those with bony fractures. Patients with tendon ruptures had a much higher median BMI of 36.0 (P < 0.0001) compared to those with patellar fractures. Obesity has been well-documented as a risk factor for tendinopathy, tendon tears, and ruptures.[25] Garner et al.[5] in a review of 726 patients found that BMI was significantly higher in patients with quadriceps tendon ruptures (30.0 ± 6.05 kg/m2) and patellar tendon ruptures (28.7 ± 4.97 kg/m2) compared to those with patellar fractures (25.0 ± 5.2 kg/m2). In addition, sex distribution was significantly different between the two groups. Tendon ruptures were significantly more common in males (M: F = 46:5), while patellar fractures had a near-equal sex distribution (M: F = 50:48) (P < 0.001). These findings reinforce that males are significantly more likely to sustain tendon ruptures.
When treating an EM rupture, the goal of orthopedic surgery is to restore knee motion and functional rehabilitation, ensuring painless and unrestricted movement. While functional knee scores, such as the Western Ontario and McMaster Universities Arthritis Index (WOMAC),[26] provide subjective assessments, they may lack sensitivity in evaluating post-surgical rehabilitation outcomes. Objective measurements of active and passive joint range of motion are commonly used as indicators of knee joint integrity.[27] The normal knee allows a passive motion from 10° of hyperextension to 134° of flexion during static examination.[28] We generally consider 90° of passive knee flexion sufficient for most daily activities; however, gait may require <90°, while activities such as climbing stairs, rising from a chair, and bathing may require between 90° and 135° of flexion. Rowe et al.[28] proposed 110° of knee flexion as a suitable goal for functional rehabilitation, aligning well with our study findings.
In our study of 149 patients with EM ruptures, we achieved a median final flexion of 115° (range: 110°–120°). Eight patients developed an extensor lag, including three with patellar fractures and five with quadriceps ruptures. One of these patients had a 30° lag, while the remainder had mild deficits. Notably, we found no significant difference in final flexion between comminuted patellar fractures (120°) and transverse fractures (115°) (P = 0.82), suggesting that if fractures are appropriately fixed and rehabilitated, knee flexion outcomes are not significantly affected by fracture type.
While previous studies have been limited by small sample sizes, the strength of our study lies in its large sample of 149 patients, all of whom received a standardized rehabilitation protocol. Our ability to assess final flexion outcomes in this cohort provides valuable insight into functional recovery following EM repair. In addition, all consecutive patients were included, including those with open fractures, which allowed for a comprehensive analysis.
However, this study has several limitations inherent to its retrospective design. Validated functional outcome scores (e.g., WOMAC) were not consistently available, and pre-operative baseline scores were not recorded; therefore, objective measures such as range of motion and complications were used to assess outcomes. In addition, although patellar fractures and tendon ruptures were managed under a common post-operative protocol, the two groups differed in baseline characteristics, particularly age and BMI. While stratified outcomes are presented, the study was not powered for multivariable modeling, limiting our ability to fully adjust for these differences. Patellar fractures were also treated with a variety of fixation constructs (K-wires, screws, plates, nitinol staples), which may influence stability and theoretical mobilization timing; however, implant-specific effects on fixation loss or final range of motion could not be assessed due to sample size. Excluding patients who were lost to follow-up or did not adhere to the standardized rehabilitation protocol may introduce selection bias. Finally, patients requiring additional procedures such as debridement may introduce confounding effects, as removal of adhesions or soft-tissue release can affect post-operative range of motion independent of the rehabilitation protocol.
Despite these limitations, our findings provide evidence that delaying mobilization is a viable option following EM repair. This study was not designed to compare early and delayed mobilization protocols or to establish the superiority of one approach over another; rather, our aim was to determine whether delayed flexion could be safely implemented without compromising functional outcomes. While there is a lack of prospective studies directly comparing early and delayed mobilization, our results support the conclusion that a conservative approach with restricted knee motion for at least 6 weeks leads to favorable long-term motion with a low rate of complications.
CONCLUSION
Our findings demonstrate that delayed mobilization – specifically delaying active flexion for 6 weeks – while allowing full weight-bearing, results in favorable postoperative outcomes, including a good range of motion and low complication rates. While early mobilization strategies have been previously promoted to accelerate recovery, recent evidence suggests that they may also increase the risk of adverse events, additional surgical interventions, and, therefore, healthcare costs. Our study supports the notion that a more conservative rehabilitation protocol is acceptable, as it appears to provide safe and effective outcomes without compromising long-term knee function.
Authors’ contributions:
TMD and DSH were responsible for the study conceptualization. TMD and JDB collected the data and drafted the manuscript. ANM contributed to data curation and critical manuscript revisions. DSH reviewed and approved the final version of the manuscript. All authors have critically reviewed and approved the final draft and are responsible for the manuscript’s content and similarity index.
Ethical approval:
The institutional Review Board Approval is not required as it is retrospective study. This study was conducted in accordance with the Declaration of Helsinki. It was approved and deemed exempt by IRB (#2022-0418) under the U.S. Department of Health and Human Services regulations for the protection of human subjects (45 CFR 46.104) on June 15, 2022.
Declaration of patient consent:
Informed consent was waived by the Institutional Ethics Committee due to the retrospective design of the study.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Conflicts of interest:
There are no conflicting relationships or activities.
Financial support and sponsorship: This study did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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