Analysis of complications and revisions after spine surgery in 270 multiple myeloma patients with spinal involvement

BACKGROUND CONTEXT

Patients with multiple myeloma (MM) are at increased risk of infections and suffer from poor bone quality due to their disseminated malignant bone disease. Therefore, postoperative complications may occur following surgical treatment of MM lesions.

PURPOSE

In this study, we aimed to determine the incidence of postoperative complications and retreatments after spinal surgery in MM patients. Additionally, we sought to identify risk factors associated with complications and retreatments.

STUDY DESIGN

Retrospective cohort study.

PATIENT SAMPLE

In total, 270 patients with MM who received surgical treatment for spinal involvement between 2008 and 2021 were included.

OUTCOME MEASURES

The incidence of perioperative complications within 6 weeks and reoperations within 2.5 years and individual odds ratios for factors associated with these complications and reoperations.

METHODS

Data were collected through manual chart review. Hosmer and Lemeshow's purposeful regression method was used to identify risk factors for complications and reoperations.

RESULTS

The median age of our cohort was 65 years (SD = 10.8), and 58% were male (n = 57). Intraoperative complications were present in 24 patients (8.9%). The overall 6-week complication rate after surgery was 35% (n = 95). The following variables were independently associated with 6-week complications: higher Genant grading of a present vertebral fracture (OR 1.41; 95% CI 1.04-1.95; p = .031), receiving intramuscular or intravenous steroids within a week prior to surgery (OR 3.97; 95% CI 1.79-9.06; p = .001), decompression surgery without fusion (OR 6.53; 95% CI 1.30-36.86; p = .026), higher creatinine levels (OR 2.18; 95% CI 1.19-5.60; p = .014), and lower calcium levels (OR 0.58; 95% CI 0.37-0.88; p = .013). A secondary surgery was indicated for 53 patients (20%), of which 13 (4.8%) took place within two weeks after the initial surgery. We additionally discovered factors associated with retreatments, which are elucidated within the manuscript.

CONCLUSION

The goal of surgical treatment for MM bone disease is to enhance patient quality of life and reduce symptom burden. However, postoperative complication rates remain relatively high after spine surgery in patients with MM, likely attributable to both inherent characteristics of the disease and patient comorbidities. The risk for complications and secondary surgeries should be explored and a multidisciplinary approach is crucial.

Neurologic Outcomes After Radiation Therapy for Severe Spinal Cord Compression in Multiple Myeloma: A Study of 162 Patients

BACKGROUND

Bone destruction is the most frequent disease-defining clinical feature of multiple myeloma (MM), resulting in skeletal-related events such as back pain, pathological fractures, or neurologic compromise including epidural spinal cord compression (ESCC). Up to 24% of patients with MM will be affected by ESCC. Radiation therapy has been proven to be highly effective in pain relief in patients with MM. However, a critical knowledge gap remains with regard to neurologic outcomes in patients with high-grade ESCC treated with radiation.

METHODS

We retrospectively included 162 patients with MM and high-grade ESCC (grade 2 or 3) who underwent radiation therapy of the spine between January 2010 and July 2021. The primary outcome was the American Spinal Injury Association (ASIA) score after 12 to 24 months, or the last known ASIA score if the patient had had a repeat treatment or died. Multivariable logistic regression was used to assess factors associated with poor neurologic outcomes after radiation, defined as neurologic deterioration or lack of improvement.

RESULTS

After radiation therapy, 34 patients (21%) had no improvement in their impaired neurologic function and 27 (17%) deteriorated neurologically. Thirty-six patients (22%) underwent either surgery or repeat irradiation after the initial radiation therapy. There were 100 patients who were neurologically intact at baseline (ASIA score of E), of whom 16 (16%) had neurologic deterioration. Four variables were independently associated with poor neurologic outcomes: baseline ASIA (odds ratio [OR] = 6.50; 95% confidence interval [CI] = 2.70 to 17.38; p < 0.001), Eastern Cooperative Oncology Group (ECOG) performance status (OR = 6.19; 95% CI = 1.49 to 29.49; p = 0.015), number of levels affected by ESCC (OR = 4.02; 95% CI = 1.19 to 14.18; p = 0.026), and receiving steroids prior to radiation (OR = 4.42; 95% CI = 1.41 to 16.10; p = 0.015).

CONCLUSIONS

Our study showed that 38% of patients deteriorated or did not improve neurologically after radiation therapy for high-grade ESCC. The results highlight the need for multidisciplinary input and efforts in the treatment of high-grade ESCC in patients with MM. Future studies will help to improve patient selection for specific and standardized treatments and to clearly delineate which patients are likely to benefit from radiation therapy.

LEVEL OF EVIDENCE

Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Low rate of return to pre-injury level of sports after multi-ligament knee injury - Functional outcomes after MLKI

BACKGROUND

Multi-ligament knee injury (MLKI) is a rare but severe injury with potential devastating complications. The primary goal of this study was to investigate return to sports and work after MLKI. Secondary outcomes were patient reported outcome measures (PROMs), treatment, time between trauma, diagnosis and treatment, and neurovascular damage.

METHOD

A database search was performed to identify all patients with MLKI in our hospital (2010-2017). Pre-defined variables were collected from patient files and questionnaires. Multiple regression analysis was used to study the relationship between different variables and PROMs.

RESULTS

31 patients were included. The overall return to sports rate after a MLKI was 88.5%, but only 23.1% returned to their pre-injury level. 83.3% of the patients were able to return to work. Multiple regression analyses led to a significant prediction model for pain during rest (F(7,16) = 2.808, p = 0.041, R² = 0.355). Within this model, a higher age was a significant predictor for higher pain scores (p = 0.002). Age was also a significant (negative) predictor within the non-significant models for IKDC (p = 0.004) and Lysholm (p = 0.024). A delay between trauma and diagnosis of more than three months was seen in 32.3% of the patients.

CONCLUSIONS

This study showed a relatively high overall return to sports and work after MLKI, but less than a quarter returned to their pre-injury level of sports. An important finding was the substantial number of patients with a delay between trauma and diagnosis. This study contributes to more awareness and knowledge about MLKI among physicians, which is essential to reduce these delays.

Are the Roland Morris Disability Questionnaire and Oswestry Disability Index interchangeable in patients after lumbar spinal fusion?

BACKGROUND

Low back pain is a common health problem for which there are several treatment options. For optimizing clinical decision making, evaluation of treatments and research purposes it is important that health care professionals are able to evaluate the functional status of patients. Patient reported outcome measures (PROMs) are widely accepted and recommended. The Roland Morris Disability Questionnaire (RMDQ) and the Oswestry Disability Index (ODI) are the two mainly used condition-specific patient reported outcomes. Concerns regarding the content and structural validity and also the different scoring systems of these outcome measures makes comparison of treatment results difficult.

OBJECTIVE

Aim of this study was to determine if the RMDQ and ODI could be used exchangeable by assessing the correlation and comparing different measurement properties between the questionnaires.

METHODS

Clinical data from patients who participated in a multicenter RCT with 2 year follow-up after lumbar spinal fusion were used. Outcome measures were the RMDQ, ODI, Short Form 36 - Health Survey (SF-36), leg pain and back pain measured on a 0-100 mm visual analogue scale (VAS). Cronbach's alpha coefficients, Spearman correlation coefficients, multiple regression analysis and Bland-Altman plots were calculated.

RESULTS

three hundred and seventy-six completed questionnaires filled out by 87 patients were used. The ODI and RMDQ had both a good level of internal consistency. There was a very strong correlation between the RMDQ and the ODI (r= 0.87; p< 0.001), and between the VAS and both the ODI and RMDQ. However, the Bland-Altman plot indicated bad agreement between the ODI and RMDQ.

CONCLUSIONS

The RMDQ and ODI cannot be used interchangeably, nor is there a possibility of converting the score from one questionnaire to the other. However, leg pain and back pain seemed to be predictors for both the ODI and the RMDQ.

Long-term (> 10 years) clinical outcomes of instrumented posterolateral fusion for spondylolisthesis

PURPOSE

Despite the rapid increase in instrumented spinal fusions for a variety of indications, most studies focus on short-term fusion rates. Long-term clinical outcomes are still scarce and inconclusive. This study investigated clinical outcomes > 10 years after single-level instrumented posterolateral spinal fusion for lumbar degenerative or isthmic spondylolisthesis with neurological symptoms.

METHODS

Cross-sectional long-term follow-up among the Dutch participants of an international multicenter randomized controlled trial comparing osteogenic protein-1 with autograft. Clinical outcomes were assessed using the Oswestry Disability Index (ODI), EQ-5D-3L and visual analogue scale (VAS) for leg and back pain, as well as questions on satisfaction with treatment and additional surgery.

RESULTS

The follow-up rate was 73% (41 patients). At mean 11.8 (range 10.1-13.7) years after surgery, a non-significant deterioration of clinical outcomes compared to 1-year follow-up was observed. The mean ODI was 20 ± 19, mean EQ-5D-3L index score 0.784 ± 0.251 and mean VAS for leg and back pain, respectively, 34 ± 33 and 31 ± 28. Multiple regression showed that diagnosis (degenerative vs. isthmic spondylolisthesis), graft type (OP-1 vs. autograft) and 1-year fusion status (fusion vs. no fusion) were not predictive for the ODI at long-term follow-up (p = 0.389). Satisfaction with treatment was excellent and over 70% of the patients reported lasting improvement in back and/or leg pain. No revision surgeries for non-union were reported.

CONCLUSION

This study showed favourable clinical outcomes > 10 years after instrumented posterolateral spinal fusion and supports spondylolisthesis with neurological symptoms as indication for fusion surgery.

Systematic review and meta-analysis of measurement properties of the Hip disability and Osteoarthritis Outcome Score - Physical Function Shortform (HOOS-PS) and the Knee Injury and Osteoarthritis Outcome Score - Physical Function Shortform (KOOS-PS)

OBJECTIVE

The aim of this systematic review and meta-analysis was to evaluate all evidence on measurement properties of the Hip disability and Osteoarthritis Outcome Score - Physical function Shortform (HOOS-PS) and the Knee Injury and Osteoarthritis Outcome Score - Physical function Shortform (KOOS-PS).

DESIGN

This study was conducted according to the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) guideline for systematic reviews of PROMs. MEDLINE, EMBASE, The Cochrane Library, CINAHL and PsychINFO through February 2019 were searched. Eligible studies evaluated patients with hip or knee complaints and described a measurement property, interpretability, feasibility, or the development of either the HOOS-PS or KOOS-PS.

RESULTS

Twenty-three studies were included. For both questionnaires, the content validity was found inconsistent and the quality evidence was moderate for a sufficient reliability and high for an insufficient construct validity. The HOOS-PS had a high quality evidence of sufficient structural validity and internal consistency (pooled Cronbach's alpha 0.80; n = 3761) and low quality evidence of sufficient measurement error and indeterminate responsiveness. Concerning the KOOS-PS, the quality evidence was high for an insufficient responsiveness, moderate for an inconsistent structural validity and internal consistency and low for an inconsistent measurement error.

CONCLUSIONS

The inconsistent evidence for content validity implies that scores on the HOOS-PS and KOOS-PS may inadequately reflect physical functioning. Furthermore, there is evidence for insufficient construct validity and responsiveness in patients with knee osteoarthritis receiving conservative treatment. Using the HOOS-PS or KOOS-PS as outcome measurement instruments for comparing outcomes, measuring improvements or benchmarking in patients with hip or knee complaints or undergoing arthroplasty should only be done with great caution.

REVIEW REGISTRATION

PROSPERO number CRD42017069539.

Patient characteristics do not predict the change in physical functioning following arthroplasty measured by the HOOS-PS and KOOS-PS

Predicting personalized outcome after arthroplasty improves shared decision-making. The aim of this paper was to determine predictors of functional outcome measured by the Hip disability and Osteoarthritis Outcome Score - Physical function Shortform (HOOS-PS) or Knee injury and Osteoarthritis Outcome Score - Physical function Shortform (KOOS-PS) in patients undergoing total hip (n = 79) or total knee arthroplasty (n = 90) respectively. Patients were assessed at baseline and following arthroplasty. A multiple regression analysis showed that the included variables predicted the change score in HOOS-PS limited (F (8,66) = 3.139, p = 0.005, adjusted R2 = 0.188) and the KOOS-PS not significantly (F (8,73) = 0.837, p = 0.573, adjusted R 2  = -0.016). Concluding, baseline characteristics cannot be used for personalized prediction using the KOOS-PS and HOOS-PS.

Primary intra-articular epithelioid sarcoma of the knee: Unusual presentation of a rare entity

We report a case of a 60-year-old female with severe and progressive pain of her right knee. Physical therapy, pain medication, and arthroscopic debridement were unsuccessful. Finally, pathological examination revealed an intra-articular epithelioid sarcoma, a rare tumor in an atypical location. Patient died within 5 months after initial admission. Despite this unusual clinical course and presentation, we would like to share the valuable clinical lessons we learned from this case. Introduction of a coordinating physician in combination with a multidisciplinary treatment regarding optimal pain management should optimize treatment results in future patients.

Kinematics of a highly congruent mobile-bearing total knee prosthesis

PURPOSE

Limited or absent axial rotation of the mobile insert of total knee prostheses could lead to high contact stresses and stresses at the bone-implant interface, which in turn might lead to implant loosening. The aim of this study was to assess knee kinematics and muscle activation and their possible change over time in patients with a highly congruent, mobile-bearing total knee prosthesis.

METHODS

A prospective series of 11 rheumatoid arthritis patients was included to participate in this fluoroscopic and EMG study; only 7 patients completed the study. Kinematic evaluations took place 7 months, 1 and 2 years post-operatively. Repeated measurements ANOVA and linear mixed-effects model for longitudinal data were used to compare the differences between the follow-ups.

RESULTS

There are no significant changes in axial rotations between follow-up moments for the femoral component as well as the mobile insert. The insert remained mobile and followed the femoral component from 0° until approximately 60° of knee flexion. Diverging and reversed axial rotations and translations were seen during the dynamic motions.

CONCLUSIONS

Knee kinematics and muscle activation do not appear to change in the first 2 post-operative years. Reversed and divergent axial rotations with increasing knee flexion indicate that as soon as the congruency decreases, the femoral component is no longer forced in a certain position by the insert and moves to a self-imposed position. At lower knee flexion angles, the femoral component might be obstructed by the highly congruent insert and therefore might not be able to move freely.

LEVEL OF EVIDENCE

Therapeutic study, Level IV.

Kinematics and early migration in single-radius mobile- and fixed-bearing total knee prostheses

BACKGROUND

The mobile-bearing variant of a single-radius design is assumed to provide more freedom of motion compared to the fixed-bearing variant because the insert does not restrict the natural movements of the femoral component. This would reduce the contact stresses and wear which in turn may have a positive effect on the fixation of the prosthesis to the bone and thereby decreases the risk for loosening. The aim of this study was to evaluate early migration of the tibial component and kinematics of a mobile-bearing and fixed-bearing total knee prosthesis of the same single-radius design.

METHODS

Twenty Triathlon single-radius posterior-stabilized knee prostheses were implanted (9 mobile-bearing and 11 fixed-bearing). Fluoroscopy and roentgen stereophotogrammetric analysis (RSA) were performed 6 and 12 months post-operatively.

FINDINGS

The 1 year post-operative RSA results showed considerable early migrations in 3 out of 9 mobile-bearing patients and 1 out of 11 fixed-bearing patients. The range of knee flexion was the same for the mobile-bearing and fixed-bearing group. The mobile insert was following the femoral component during motion.

INTERPRETATION

Despite the mobile insert following the femoral component during motion, and therefore performing as intended, no kinematic advantages of the mobile-bearing total knee prosthesis were seen. The fixed-bearing knee performed as good as the mobile-bearing knee and maybe even slightly better based on less irregular kinematics and less early migrations.

The quality of bone surfaces may govern the use of model based fluoroscopy in the determination of joint laxity

The assessment of knee joint laxity is clinically important but its quantification remains elusive. Calibrated, low dosage fluoroscopy, combined with registered surfaces and controlled external loading may offer possible solutions for quantifying relative tibio-femoral motion without soft tissue artefact, even in native joints. The aim of this study was to determine the accuracy of registration using CT and MRI derived 3D bone models, as well as metallic implants, to 2D single-plane fluoroscopic datasets, to assess their suitability for examining knee joint laxity. Four cadaveric knees and one knee implant were positioned using a micromanipulator. After fluoroscopy, the accuracy of registering each surface to the 2D fluoroscopic images was determined by comparison against known translations from the micromanipulator measurements. Dynamic measurements were also performed to assess the relative tibio-femoral error. For CT and MRI derived 3D femur and tibia models during static testing, the in-plane error was 0.4 mm and 0.9 mm, and out-of-plane error 2.6 mm and 9.3 mm respectively. For metallic implants, the in-plane error was 0.2 mm and out-of-plane error 1.5 mm. The relative tibio-femoral error during dynamic measurements was 0.9 mm, 1.2 mm and 0.7 mm in-plane, and 3.9 mm, 10.4 mm and 2.5 mm out-of-plane for CT and MRI based models and metallic implants respectively. The rotational errors ranged from 0.5° to 1.9° for CT, 0.5-4.3° for MRI and 0.1-0.8° for metallic implants. The results of this study indicate that single-plane fluoroscopic analysis can provide accurate information in the investigation of knee joint laxity, but should be limited to static or quasi-static evaluations when assessing native bones, where possible. With this knowledge of registration accuracy, targeted approaches for the determination of tibio-femoral laxity could now determine objective in vivo measures for the identification of ligament reconstruction candidates as well as improve our understanding of the consequences of knee joint instability in TKA.

No differences in in vivo kinematics between six different types of knee prostheses

PURPOSE

The aim of this study was to compare a broad range of total knee prostheses with different design parameters to determine whether in vivo kinematics was consistently related to design. The hypothesis was that there are no clear recognizable differences in in vivo kinematics between different design parameters or prostheses.

METHODS

At two sites, data were collected by a single observer on 52 knees (49 subjects with rheumatoid arthritis or osteoarthritis). Six different total knee prostheses were used: multi-radius, single-radius, fixed-bearing, mobile-bearing, posterior-stabilized, cruciate retaining and cruciate sacrificing. Knee kinematics was recorded using fluoroscopy as the patients performed a step-up motion.

RESULTS

There was a significant effect of prosthetic design on all outcome parameters; however, post hoc tests showed that the NexGen group was responsible for 80% of the significant values. The range of knee flexion was much smaller in this group, resulting in smaller anterior-posterior translations and rotations.

CONCLUSION

Despite kinematics being generally consistent with the kinematics intended by their design, there were no clear recognizable differences in in vivo kinematics between different design parameters or prostheses. Hence, the differences in design parameters or prostheses are not distinct enough to have an effect on clinical outcome of patients.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

The Femoral Epicondylar Frame to track femoral rotation in optoelectronic gait analysis

Relative movement of skin markers to underlying bone limits a valid interpretation of axial femorotibial rotation in noninvasive optoelectronic gait analysis. A distal femoral clamp is a practical solution for thigh marker placement, however, existing devices are still susceptible to measurement errors at increased angles of knee flexion. We developed the Femoral Epicondylar Frame (FEF), which should result in less femoral rotational measurement error due to its anatomic fitting and controlled pressure adjustment. Seven subjects with a total knee replacement in situ, mean age 71 years, mean body mass index 28, were equipped with the frame mounted with a set of tantalum markers. Fluoroscopic data was collected during a step-up motion. A three-dimensional model fitting technique was used to compare the in vivo position and orientation of the frame and the femoral prosthesis component of the prosthesis. The frame rotational measurement error appeared to be linearly dependent on the knee flexion angle. When considering knee flexion angles lower than 40° of flexion, the highest measurement error was 3.3° on average, with an absolute extreme of 6.2°. It is concluded that the accuracy of the FEF is sufficient to evaluate axial knee rotation with optoelectronic gait analysis at group level in clinical studies.

Mobile bearing knee kinematics change over time. A fluoroscopic study in rheumatoid arthritis patients

BACKGROUND

In a previous fluoroscopy study the motion of a mobile bearing total knee prosthesis was evaluated. That study showed that the axial rotation of the insert was limited. Three possible explanations are given for the limited rotation: low conformity between the femoral component and insert, the fixed anterior position of the insert-tibia pivot point leading to impingement and fibrous tissue formation. While the effect of the conformity on the axial rotation will not change over time, the effect of impingement and fibrous tissue is likely to increase, and thereby further decreasing the axial rotation.

METHODS

In order to accurately assess changes in axial rotation over time in a mobile bearing total knee prosthesis rheumatoid arthritis patient group, patients were evaluated 8 months and 3 years postoperatively using fluoroscopy.

FINDINGS

In comparison with the 8 months evaluation, the rotation of the femoral component (range: -10.8 degrees to 2.8 degrees) and the insert (range: -5.9 degrees to 1.4 degrees) were further limited at 3 years (respectively, -5.9 degrees to 4.9 degrees and -2.8 degrees to 5.4 degrees). Patterns of axial rotation for the femoral component and insert varied considerably between the trials within patients while at the 8 months evaluation no significant difference within patients was observed.

INTERPRETATION

This study shows the importance of re-evaluating knee kinematics over time. The axial rotation of both the femoral component as the insert decreased over time, indicating a kinematic change caused by intrinsic factors. The decline in rotation of the insert could be explained by increased impingement and the formation of fibrous tissue.

Knee rotation during a weightbearing activity: influence of turning

Kinematic studies, in which mobile- and fixed-bearing total knee arthroplasty (TKA) were compared, showed controversial results with respect to axial femorotibial rotation. However, all studies focused only on straight ahead tasks, which may underestimate possible differences in freedom of rotation. The purpose of this study was to investigate the influence of turning on normal axial knee rotation. If large differences across tasks were to be found, this would support the use of this task in the evaluation of in-vivo TKA kinematics. In 15 healthy persons, crossover and sidestep turns were added to a standardized chair rise. Three-dimensional knee angles were recorded using an optoelectronic motion analysis system, and a noninvasive epicondylar frame was developed to track the femur. Compared to knee rotation during the straight ahead task, average peak tibial internal rotation increased during a crossover turn (p<0.001), as did peak external tibia rotation during a sidestep turn (p<0.001). The combined range of axial rotation for both turning tasks together was 20.9 degrees , versus 13.5 degrees for the straight ahead task (p<0.001). The turning maneuvers in this study induced a large range of axial knee rotation, so they could be important in studies comparing freedom of rotation in mobile- and fixed-bearing TKA.

Knee varus-valgus motion during gait--a measure of joint stability in patients with osteoarthritis?

OBJECTIVE

To determine the validity of varus-valgus motion as a measure of knee joint stability by establishing the relationship of varus-valgus motion with muscle strength, joint proprioception, joint laxity and skeletal alignment in patients with knee osteoarthritis (OA).

METHODS

Sixty-three patients with OA of the knee were tested. Varus-valgus motion was determined with a video-based optoelectronic gait analysis system. Muscle strength was measured using a computer-driven isokinetic dynamometer. Proprioceptive acuity was assessed by establishing the joint motion detection threshold in the anterior-posterior direction. Laxity was assessed using a device which measures the passive angular deviation of the knee in the frontal plane. Alignment was assessed using a goniometer. Regression analyses were performed to assess the relationship between varus-valgus motion, muscle strength, joint proprioception, joint laxity and skeletal alignment.

RESULT

Varus-valgus motion was not related to muscle strength, joint proprioception, joint laxity and skeletal alignment.

CONCLUSIONS

Knee joint stability cannot be measured as varus-valgus motion. Rather, a number of independent factors seem to contribute to the process of stabilization of the knee joint.

Varus–valgus motion and functional ability in patients with knee osteoarthritis

Objective:

To assess the relationship between knee varus–valgus motion and functional ability, and the impact of knee varus–valgus motion on the relationship between muscle strength and functional ability in patients with osteoarthritis (OA) of the knee.

Methods:

Sixty-three patients with knee OA were tested. Varus–valgus motion was assessed by optoelectronic recording and three-dimensional motion analysis. Functional ability was assessed by observation, using a 100 m walking test, a Get Up and Go test, and WOMAC questionnaire. Muscle strength was measured by a computer-driven isokinetic dynamometer. Regression analyses were performed to assess the relationships between varus–valgus motion and functional ability, and to assess the impact of varus–valgus motion on the relationship between muscle strength and functional ability.

Results:

In patients with high varus–valgus range of motion, muscle weakness was associated with a stronger reduction in functional ability (ie, longer walking time and Get Up and Go time) than in patients with low varus–valgus range of motion. A pronounced varus position and a difference between the left and right knees in varus–valgus position were related with reduced functional ability.

Conclusions:

In patients with knee OA with high varus–valgus range of motion, muscle weakness has a stronger impact on functional ability than in patients with low varus–valgus range of motion. Patients with knee OA with more pronounced varus knees during walking show a stronger reduction in functional ability than patients with less pronounced varus knees or with valgus knees.