Abstract
Purpose
To examine outcomes following surgically treated multiligamentous knee injuries (MLKIs) in obese versus nonobese patients.
Methods
Patients who were surgically treated for MLKIs between 2008 and 2021 were included in this study. Patients were divided into 2 groups and classified as obese (body mass index ≥30) or nonobese. The following patient-reported outcome measures were collected: the visual analog scale for pain, the International Knee Documentation Committee subjective score, and the Lysholm knee scoring scale. Complications such as revision ligamentous reconstruction, conversion to total knee arthroplasty (TKA), infection, and arthrofibrosis were also documented.
Results
A total of 88 patients (88 knees; 43 obese, 45 nonobese) were included in the final analysis. The mean overall age was 34.3 ± 12.7 years (10-61 years), and there were 30 women and 58 men included in this study cohort. The mean follow-up for the patients who did not receive a revision or TKA was 9.2 years (range, 3.4-15.3 years). There were no differences seen between groups for age, sex, mechanism of injury, neurovascular status, concomitant injuries, frank knee dislocations, surgical staging, or external fixator application. However, the mean follow-up in the nonobese group was higher than in the obese group (9.7 vs 8.3 years, P = .003). The nonobese cohort had significantly more open injuries compared to the obese cohort (11.1% vs 2.3%, P = .05). Although there were no differences seen in conversion to TKA or arthrofibrosis, the obese cohort had a higher rate of ligament failure (30.2% vs 8.9%, P = .02) and infection (14% vs 2.2%, P = .05). Additionally, the obese cohort had worse visual analog scale for pain scores (4.4 vs 2.2, P = .002), lower International Knee Documentation Committee scores (50.3 vs 74.6, P < .001), and lower Lysholm scores (59.9 vs 80.6, P = .004) at final follow-up compared to the nonobese cohort.
Conclusions
Obese patients had significantly higher rates of ligament failure and infection rates, higher pain scores, and worse patient-reported outcomes than nonobese patients following surgically treated MLKIs.
Level of Evidence
Level III, retrospective cohort study.
Multiligamentous knee injuries (MLKIs) are rare and complex injuries typically resulting from high- or low-energy trauma.1, 2, 3, 4 These injuries are commonly linked to acute knee dislocations (KDs).5,6 The incidence of MLKIs is reported to be less than 0.02% of all orthopaedic injuries, although this figure may be underestimated due to spontaneous knee reductions and missed diagnoses.1,5, 6, 7
Obesity has been increasingly recognized as a major factor influencing both the occurrence and outcomes of MLKIs.4,8, 9, 10, 11, 12, 13 Obesity is associated with a higher risk for low-energy KDs.2,4,5,10,12, 13, 14, 15 Additionally, each increasing level of obesity imposes a greater risk of MLKIs following low-energy trauma.2,4,9,10,12, 13, 14, 15 Furthermore, obesity has been shown to be associated with decreased healing rates, a higher risk of postoperative infection, persisting neurovascular deficits, prolonged recovery times, difficulties with rehabilitation, and lower patient-reported outcomes (PROs).3, 4, 5,8,10,12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23
In a case series with a mean 7-year follow-up, Tan et al.13 noted that each 10-kg/m2 increase in obesity was associated with various significant decreases in Knee injury and Osteoarthritis Outcome Score (KOOS) subscales at the final follow-up. Other studies focused exclusively on the obese patient populations and/or had a mean <5-year final follow-up.14,15,17,20 Nonetheless, the full extent of the effect of increased or increasing body mass index (BMI) on mid- to long-term outcomes following MLKIs remains unclear, especially when directly comparing a nonobese to an obese cohort with similar follow-up times.
The purpose of this study was examine outcomes following surgically treated MLKIs in obese versus nonobese patients. We hypothesize that obese patients will experience significantly inferior outcomes compared to their nonobese counterparts.
Methods
Study Design
Institutional review board approval was obtained before the start of this study. This is a single-center retrospective cohort study comparing outcomes between obese and nonobese patients who underwent surgical treatment for traumatic MLKIs, managed by the senior author (S.J.K.). The study included all patients who received primary multiligamentous knee surgery from 2008 to 2021. Patients were excluded if they lacked operative information or required a below-knee amputation following their multiligamentous knee surgery. Of note, this study includes patients who have been previously reported in a similar study examining patients with MLKIs with or without frank knee dislocations.24
Data Collection
A retrospective chart review was conducted to identify patients using Current Procedural Terminology codes specific to ligamentous knee surgeries (e.g., 29888 for anterior cruciate ligament [ACL] reconstruction/repair, 29889 for posterior cruciate ligament [PCL] reconstruction/repair, 27405 for collateral ligament reconstruction/repair). Patients were then contacted to obtain postoperative subjective outcomes. After identifying patients, the electronic medical record was reviewed to collect demographic information, intraoperative characteristics, and postoperative complications. Demographic information included patient age, sex, BMI, injury velocity, time from injury to surgery, and mechanism of injury. Operative and treatment-related information included details on cartilage/meniscal injury, specific ligamentous injuries, documentation of knee dislocations via presenting radiographs or postreduction notes in the emergency department, use of external fixator, staged versus nonstaged procedures, and any concomitant neurovascular or other orthopaedic/nonorthopaedic injuries. Ligamentous injury pattern was graded using the Schenck classification25; furthermore, KD-III injury patterns were further subclassified into KD-IIIM or KD-IIIL. Following data collection, patients were placed in 2 groups: the obese cohort (BMI ≥30) and a nonobese cohort.
Outcomes and Follow-Up
The following validated PRO measures were documented: the visual analog scale for pain (VAS),26 the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation,27 and the Lysholm Knee Scoring Scale.28 Complications and the need for further knee surgery were also recorded. For this study, outcomes were specifically analyzed to compare results between obese and nonobese patients. Final follow-up was determined based on the date when these PRO measures were completed or the occurrence of revision ligamentous surgery or total knee arthroplasty (TKA).
Surgical Techniques
All ligamentous reconstructions were performed using allografts. An external fixator was applied in cases where the patient had a popliteal artery injury, open injuries, concomitant femoral and/or tibial fracture above the joint line, an unstable intra-articular fracture, or if reduction was unable to be maintained with a brace/splint.
KD-III, KD-IV, and KD-V injuries (involving 3 or more ligaments) were typically treated in stages. For KD-III or KD-V injuries involving only 3 structures, the PCL and lateral collateral ligament (LCL) ± posterolateral corner (PLC) or the medial collateral ligament (MCL) ± posteromedial complex (PMC) was addressed during the initial procedure, with ACL surgery staged for a later date. For KD-IV injuries or KD-V injuries involving all ligamentous structures, the PCL and MCL ± PMC were treated first, with ACL and LCL ± PLC surgery staged for later.
PCL reconstruction was achieved using an Achilles allograft with a bone plug into the proximal posterior tibia and a PCL tightrope device (Arthrex). An interference screw was used for femoral fixation. Final PCL fixation was done with the knee held at 60° of flexion and 1 cm of anterior translation tensioning the allograft on the femoral side. The MCL/PMC reconstruction utilized a semitendinosus for the MCL and gracilis for the corner. Distally, the graft was fixed just proximal to the pes anserinus. Proximally, the graft was fixed at its isometric point just posterior to the medial epicondyle along Blumensaat’s line, which was visualized fluoroscopically. Final MCL/PMC fixation was achieved with the knee in extension, varus force, and slight external rotation. For the LCL/PLC reconstruction, before tunnel drilling on the lateral side, a peroneal nerve neurolysis was performed and the nerve was protected throughout the tunnel preparation and reconstruction. A femoral socket was placed at the popliteal tendon’s insertion, just posterior to the lateral epicondyle. While protecting posterior neurovascular structures, a tibial tunnel was then drilled from anterior to posterior at the proximal, lateral face of the tibia, aiming to the posterior, proximal, lateral corner. Next, with fluoroscopic guidance, an anterolateral-to-posteromedial fibular tunnel was established for eventual graft passage. Two allografts, a semitendinosus and gracilis graft, were then inserted and rigidly fixed in the femur. The LCL limb of the graft, most often the semitendinosus graft, was then passed underneath the native popliteus and the iliotibial band and shuttled from anterior to posterior through the fibular tunnel. With the leg in extension, valgus, and slight internal rotation, the graft was fixed with an interference screw. The remaining semitendinosus graft, which passed through the fibula, was combined with the other graft, most often the gracilis, from the femoral socket and passed through the tibia from posterior to anterior. With the leg again in extension, valgus, and slight internal rotation, an interference screw was placed in the tibial tunnel to affix both grafts in place. ACL reconstruction was achieved using a posterior tibialis tendon allograft. Final ACL fixation was achieved using rigid fixation distally and adjustable loop fixation proximally utilizing a femoral tight rope (Arthrex). With the knee held in extension, the proximal adjustable loop device was tensioned for final ACL fixation.
The postoperative rehabilitation was highly variable and dependent on the surgical intervention and surgeon preference.
Statistical Analysis
Patients were grouped based on BMI categories: (1) normal/overweight and (2) obese; 1 patient whose BMI was considered underweight was included in the normal group. Continuous variables were represented as mean ± standard deviation (range). Categorical variables were represented as absolute frequency (percentage). For continuous variables, independent t tests were conducted, and for categorical variables, χ2 tests of independence/Fisher exact tests were conducted. Univariate analyses were conducted on patient demographics, operative characteristics, and outcomes between the BMI groups. All analyses used 2-tailed tests with an α criterion of 0.05 for significance. Statistical analyses were conducted using SPSS version 27 (IBM).
Results
Final Patient Population
A total of 188 patients received a primary multiligamentous knee surgery between 2008 and 2021. Of the total potentially eligible patients, 88 were included in the final data analysis (Fig 1). Sixty-six patients (35.1%) had inaccurate contact information. Twenty-nine patients (15.4%) had correct contact information but were unable to be contacted following multiple attempts. Three patients (1.60%) were found to be deceased, and 2 patients (1.06%) did not have any available operative information on their medical record.
Fig 1.
Flowchart describing patient inclusion.
Demographic and Injury-Specific Factors
Preoperative patient characteristics are summarized in Table 1. There were no differences seen in age, time from initial injury to surgery, mechanism of injury, or injury velocity. The nonobese cohort had a BMI of 25.0, and the obese cohort had a BMI of 36.8.
Table 1.
Demographic and Injury-Specific Factors
| Characteristic | Nonobese (n = 45) | Obese (n = 43) | P Value |
|---|---|---|---|
| Body mass index | 25.0 ± 2.8 (18.2-29.7) | 36.8 ± 5.9 (30.0-52.9) | NA |
| Age, y | 34.2 ± 14.6 (10-63) | 35.5 ± 11.7 (19-60) | .64 |
| Sex, female | 31 (69) | 27 (63) | .55 |
| Injury-to-surgery, d | 68.8 ± 124 (2-687) | 74.7 ± 121 (0-623) | .82 |
| Mechanism of injury | .46 | ||
| MVC | 14 (31) | 15 (35) | |
| MCA | 11 (24) | 6 (14) | |
| AvP | 5 (11) | 8 (19) | |
| AvB | 1 (2) | 1 (2) | |
| Fall | 8 (18) | 8 (19) | |
| Sports | 3 (7) | 3 (7) | |
| Crush | (0) | 2 (5) | |
| Assault | 3 (7) | (0) | |
| Velocity, high energy | 31 (69) | 31 (72) | .82 |
NOTE. Data represented as mean ± standard deviation (range) or absolute frequency (percentage).
AvB, automobile versus bicycle; AvP, automobile versus pedestrian; MCA, motorcycle accident; MVC, motor vehicle collision; NA, not applicable.
Operative Characteristics and Concomitant Pathology
Operative factors are summarized in Table 2. There were significantly more patients in the nonobese group who had open injuries (5 [11%] vs 1 [2%], P = .05). There were no differences seen in neurovascular status, meniscal/chondral injuries, nonligament knee injuries, KD grades, frank dislocations, or staged procedures with or without the use of external fixation.
TABLE 2.
Operative Factors
| Factor | Nonobese (n = 45) | Obese (n = 43) | P Value |
|---|---|---|---|
| Peroneal nerve injury | 3 (7) | 5 (12) | .48 |
| Popliteal artery injury | 5 (11) | 4 (9) | ≥.999 |
| Meniscal injury | 12 (27) | 15 (35) | .86 |
| Medial | 6 (13) | 7 (16) | |
| Lateral | 4 (9) | 5 (12) | |
| Bilateral | 2 (4) | 3 (7) | |
| Schenck classification | .64 | ||
| KD-I | 16 (36) | 13 (30) | |
| KD-II | 5 (11) | 4 (9) | |
| KD-IIIM | 7 (16) | 11 (26) | |
| KD-IIIL | 7 (16) | 10 (23) | |
| KD-IV | 2 (4) | 1 (2) | |
| KD-V | 8 (18) | 4 (9) | |
| Frank dislocations | 18 (40) | 18 (42) | .86 |
| Open injury | 5 (11) | 1 (2) | .05 |
| External fixation | 11 (24) | 11 (26) | ≥.999 |
| Staged procedures | 19 (42) | 21 (49) | .67 |
| Polytrauma∗ | 33 (73) | 26 (61) | .26 |
NOTE. Data represented as absolute frequency (percentage).
KD, knee dislocation.
Classified as having additional orthopaedic trauma (i.e., pelvic/acetabular fracture, distal radius fracture, etc.) and/or nonorthopaedic trauma (i.e., bowel laceration, maxillofacial injury, etc.).
Postoperative Complications
Postoperative complications and graft failure rate are summarized in Table 3. The overall complication rate was higher in the obese cohort (19 [44%] vs 11 [24%], P = .05). Compared to the nonobese cohort, the obese cohort had a higher incidence of infection (6 [14%] vs 1 [2%], P = .05) as well as ligament failure (13 [30%] vs 4 [9%], P = .02). There were no differences seen in postoperative arthrofibrosis or conversion to TKA.
Table 3.
Postoperative Complications and Graft Failure Rate∗
| Outcome | Nonobese (n = 45) | Obese (n = 43) | P Value |
|---|---|---|---|
| Complications | 11 (24) | 19 (44) | .05 |
| TKA conversion | 2 (4) | 3 (7) | .67 |
| Infection | 1 (2) | 6 (14) | .05 |
| Arthrofibrosis | 5 (11) | 3 (7) | .71 |
| Ligament failure | 4 (9) | 13 (30) | .02 |
NOTE. Data represented as mean ± standard deviation (range) or absolute frequency (percentage).
TKA, total knee arthroplasty.
Unrelated to scheduled staged procedures.
Postoperative Patient-Reported Outcomes
PROs are summarized in Table 4. The nonobese cohort had higher IKDC subject scores (74.6 ± 22.5 [11.5-100] vs 50.3 ± 24.8 [3.4-95.4], P < .001) and Lysholm scores (80.6 ± 20.2 [27-100] vs 59.9 ± 30.8 [4-99], P = .002), as well as lower VAS pain levels (2.2 ± 2.5 [0-9] vs 4.4 ± 2.9 [0-10], P = .004) at final follow-up. Of note, the nonobese cohort had a significantly longer follow-up (9.7 ± 4.3 [3.4-15.3] years vs 8.3 ± 4.1 [3.4-14.2] years, P = .003).
Table 4.
Patient-Reported Outcomes∗
| Outcome | Nonobese (n = 39) | Obese (n = 27) | P Value |
|---|---|---|---|
| Follow-up, y | 9.7 ± 4.3 (3.4-15.3) | 8.3 ± 4.1 (3.4-14.2) | .003 |
| IKDC | 74.6 ± 22.5 (11.5-100) | 50.3 ± 24.8 (3.4-95.4) | <.001 |
| Lysholm | 80.6 ± 20.2 (27-100) | 59.9 ± 30.8 (4-99) | .002 |
| VAS | 2.2 ± 2.5 (0-9) | 4.4 ± 2.9 (0-10) | .004 |
NOTE. Data represented as mean ± standard deviation (range) or absolute frequency (percentage).
IKDC, International Knee Documentation Committee; VAS, visual analog scale.
Unrelated to scheduled staged procedures.
Univariate and Multivariate Analyses
Regression analyses were performed. Multivariate analyses for both the IKDC and VAS scores are described in Table 5. It was found that increasing age was associated with lower IKDC scores and higher pain levels (P < .05) on multivariate analysis. However, there were no associations between inferior scores or adverse outcomes regarding other demographic or intraoperative parameters such as sex, mechanism of injury, neurovascular status, meniscal/cartilage status, external fixator application, or Schenck classification on univariate and/or multivariate analyses.
Table 5.
Multivariate Regression Analysis for the International Knee Documentation Committee Subjective and Visual Analog Scale Scores
| Variable | B | 95% Confidence Interval | P Value |
|---|---|---|---|
| International Knee Documentation Committee Subjective | |||
| Age | –0.593 | –1.018 to –0.169 | .006 |
| ACL injury | –15.074 | –36.664 to 6.515 | .17 |
| Neurovascular injury | –1.332 | –12.670 to 15.334 | .85 |
| Frank dislocation | –8.565 | –23.174 to 6.063 | .25 |
| Open injury | –4.292 | –16.992 to 25.577 | .69 |
| Meniscal/chondral | –4.994 | –8.836 to 18.824 | .48 |
| Visual analog scale | |||
| Age | 0.783 | 0.185 to 1.112 | .01 |
| Injury-to-surgery | 0.004 | –0.007 to 0.142 | .90 |
| Frank dislocation | 1.153 | –0.249 to 2.555 | .11 |
| Open injury | 0.009 | –2.184 to 2.165 | .99 |
| Meniscal/chondral | 0.463 | –1.954 to 1.029 | .54 |
Discussion
The most important finding in this study is that obese patients had inferior subjective outcomes and higher complication rates compared to nonobese patients. Additionally, patients in the obese cohort had a higher risk of graft failure. Furthermore, despite having more open injuries in the nonobese group, the obese cohort still had a higher rate of postoperative infection. Additionally, other than the 2 groups having different BMIs, the demographic and operative parameters between the 2 groups were comparable outside of the nonobese group having a longer final follow-up. However, although the final follow-up for the nonobese cohort was significantly longer, they still had superior outcomes.
In a case series examining mid- to long-term outcomes following MLKIs, Tan et al.13 showed that at mean 7-year follow-up, PROs were negatively affected for each 10-kg/m2 increase in BMI, including Tegner activity levels, and 4 of the 5 subscales of the KOOS. Although we did not capture activity levels or KOOS scores, we still found that patients in the obese group had significantly worse PROs, nonetheless. Additionally, we were able to separate patients into 2 definitive groups based on BMI for our comparisons.
In a systematic review examining 10 studies, Smith et al.29 found that patients who had a BMI of ≥35 had worse Lysholm and IKDC scores at mid- to long-term follow-up. Additionally, they describe worse outcomes in patients over 30 years old. We were able to find similar findings in this present study. They also found that patients with concomitant cartilage damage, combined medial and lateral meniscal damage, KDs that were unable to spontaneously reduce, and KDs associated with polytrauma exhibited inferior outcomes.29 Unfortunately, we were unable to elucidate similar findings. A possible explanation is that the present study may not have been powered enough to determine more significant findings on both uni- and multivariate analyses.
In this present study, it was found that obese patients had a higher graft failure rate compared to nonobese patients. Although well-documented literature correlates obesity with higher complication rates following MLKI surgery,10,12,13,15,19,30 there appears to be a paucity of literature describing a correlation between BMI and graft failure rates following surgically treated MLKIs. In a case series examining long-term outcomes following surgically treated MLKIs, Boos et al.31 found that only 3.6% of patients underwent revision ligamentous surgery, and 10.9% of patients received TKA at final follow-up. This present study showed similar rates of conversion to TKA, with significantly more patients in the obese group requiring revision surgery.
In a retrospective review of 143 patients, Lian et al.10 found that patients in their obese cohort had a higher risk of wound infections. Similarly, in our study, it was found that patients in the obese cohort had a higher postoperative infection rate despite having fewer open injuries. It is possible that patients in the obese cohort had a higher postoperative infection that may have been due to obese patients tending to have other comorbidities such as type 2 diabetes mellitus and cardiovascular disease.32
MLKIs and frank knee dislocations have been shown to result from ultra-low-velocity trauma in the obese patient population.4,5 In this present study, we were unable to make the connection between BMI and mechanism of injury, likely due to ≥70% of the patients sustaining their injury following higher-energy traumas. Although a high percentage of patients sustained MLKIs from lower-energy traumas such as falls and crush injuries, there was still a comparable number in each group. Furthermore, it is possible that this study was not powered to determine a difference in mechanism of injury between cohorts.
Reported rates of vascular injury following KDs have been reported between 3% and 18%.3,30 In a retrospective cohort study examining 19,087 patients with frank knee dislocations, Johnson et al.19 found that the incidence of vascular injury requiring intervention increased as BMI increased. Furthermore, when excluding patients with vascular injuries, their study found that obese patients had higher average hospital stay costs. Although we were unable to find a relationship between BMI and vascular injuries, it is likely due to not having sufficient power to make this comparison in our cohort.
In a multicenter study examining 190 consecutive patients, Bi et al.7 found that increased BMI was not associated with an increased risk of postoperative arthrofibrosis requiring a manipulation under anesthesia following MLKI surgery. Moreover, numerous studies have found a relatively wide range of the rate of arthrofibrosis following surgically treated MLKIs (3/57%).33, 34, 35, 36 Both groups showed comparable rates of arthrofibrosis in the postoperative period that fell within the range of what has been previously described.
Regarding age, it was found in our regression analyses that increasing age was associated with inferior subjective outcomes. Specifically, older age was associated with lower IKDC subjective scores and higher VAS pain scores. A study performed by Levy et al.37 showed that patients over the age of 30 years had inferior PROs following MLKI surgery.
It is well documented that patients with concomitant meniscal/chondral pathology have inferior patient outcomes in the setting of surgically treated MLKIs.38,39 In a study examining 121 patients, King et al.39 found that patients who had meniscal and/or chondral damage in addition to an MLKI had significantly lower IKDC scores. This study was unable to find a relation between meniscal/chondral injuries and outcomes, which may have been due to underpowering.
In the present study, a comparable number of patients received an external fixator at the time of injury and/or underwent a staged procedure. We could not find a correlation between external fixator application or staged procedures with inferior patient outcomes. It has been described previously that patients who received an external fixator or underwent a staged procedure still had satisfactory postoperative outcomes.40
This study highlights the fact that obese patients do not do as well as nonobese patients following surgically treated MLKIs. Although the standard of care for MLKIs is ligamentous reconstruction and/or repair, it is important to note that certain patient-specific factors may result in lower patient outcomes compared to others receiving similar treatment. Further research is needed to refine the treatments for such complex ligamentous pathology, which will hopefully result in more satisfactory outcomes for certain patient populations, namely, obese patients following MLKIs.
Limitations
This study was not without limitations. First, the retrospective nature of this study subjects it to selection bias. Although all available patients were included in this study, and a large percentage of patients were unable to be contacted, the results may be over- or understated. Obtaining patient outcomes via telephone subjects that data to recall bias. Additionally, although all patients were surgically treated by a single surgeon, there was no uniform postoperative rehabilitation process. Due to the complexity of most of the injuries, with a large percentage being polytrauma patients following high-energy injuries, establishing a definitive rehabilitation protocol that accommodates all patients was impractical. Moreover, the findings of this study may not be widely generalizable, as the procedures were performed by only one surgeon. The final follow-up was significantly higher in the nonobese cohort, which may have impacted the PROs. Lastly, there were no objective outcomes included in this study, nor were there any preoperative subjective outcomes. So, we are unable to determine how much these 2 groups improved clinically at final follow-up or how much they subjectively improved from initial injury.
Conclusions
Obese patients had significantly higher rates of ligament failure and infection rates, higher pain scores, and worse PROs than nonobese patients following surgically treated MLKIs.
Disclosures
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: A.D.C. has received funding grants from Arthrex and Medical Device Business Services; has received speaking and lecture fees from Arthrex, Smith & Nephew, Medwest Associates, Micromed, and Saxum Surgical; has received travel reimbursement from Arthrex, Smith & Nephew, Medwest Associates, and Stryker. All other authors (A.V.D., W.A.W., B.J.K., J.A.C., S.J.K.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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