Knee OA: Which patients are unlikely to benefit from manual PT and exercise?
A preliminary clinical prediction rule uses 3 patient attributes to predict who will fare better with alternative treatments.
TABLE 2 presents prognostic accuracy profiles for each predictor in the CPR; TABLE 3 summarizes the accuracy for each level of the multivariate CPR. Values in TABLE 3 reflect complete sets of data for the 3 predictors found for 50 patients. Of those 50 patients, 6 (12%) were in the nonsuccess group.
TABLE 2
Prognostic accuracy statistics for individual predictors
| Predictor | Sensitivity (95% CI) | Specificity (95% CI) | Positive likelihood ratio (95% CI) | Posttest probability of nonsuccess* |
|---|---|---|---|---|
| Height ≥1.71 m | 0.65 (0.41-0.83) | 0.77 (0.67-0.85) | 2.86 (1.69-4.86) | 37% |
| ACL laxity | 0.27 (0.10-0.57) | 0.93 (0.83-0.97) | 3.68 (0.96-14.19) | 43% |
| Pain with passive patellofemoral glide in any direction | 0.71 (0.35-0.92) | 0.61 (0.47-0.74) | 1.84 (1.03-3.31) | 27% |
| ACL, anterior cruciate ligament; CI, confidence interval. *Assumes pretest probability of nonsuccess=17% (incidence in this sample). | ||||
With any 2 of the 3 tests positive, the CPR yielded a sensitivity of 83% (95% CI, 44%-97%), specificity of 98% (95% CI, 88%-100%), and positive likelihood ratio of 36.7 (95% CI, 5.1-263.0). Only 2 patients out of 50 were misclassified (one false positive and one false negative) at this level of the CPR, yielding an overall prognostic accuracy of 96% (95% CI, 87%-99%). Application of the positive likelihood ratio for a patient with any 2 positive tests yielded a posttest probability of 88% for nonsuccess with this treatment.
TABLE 3
Prognostic accuracy statistics for 3-level clinical prediction rule
| CPR level | Sensitivity (95% CI) | Specificity (95% CI) | Positive likelihood ratio (95% CI) | Posttest probability of nonsuccess* |
|---|---|---|---|---|
| All 3 tests positive | 0.21 (0.05-0.58) | 0.99 (0.90-1.00) | 19.29 (0.87-428.09) | 80% |
| At least 2 tests positive | 0.83 (0.44-0.97) | 0.98 (0.88-1.00) | 36.67 (5.11-263.01) | 88% |
| At least 1 test positive | 0.92 (0.56-0.99) | 0.48 (0.34-0.62) | 1.78 (1.26-2.52) | 27% |
| CI, confidence interval; CPR, clinical prediction rule. *Assumes pretest probability of nonsuccess=17% (incidence in this sample). | ||||
In the sensitivity analysis, the CPR performed similarly well for patients in each of the 2 original studies when applied separately to the groups of patients. Among the 30 patients from the first trial2 who had data for all 3 predictors in the CPR, only one was misclassified (a false positive), yielding a prognostic accuracy of 97% (95% CI, 83%-99%). Among the 20 patients from the second trial1 who had data for all 3 predictors, only one was misclassified (a false negative), yielding a prognostic accuracy of 95% (95% CI, 76%-99%).
DISCUSSION
Family physicians and physical therapists should be able to discuss with confidence how any given patient with knee OA will likely respond to treatment options. Our study is a preliminary step toward defining the population of patients with knee OA who are unlikely to benefit from manual physical therapy and exercise. We found such patients to be those with height >1.71 m, ACL laxity, and pain with passive glides of the patellofemoral joint.
A limitation of our study is the retrospective nature of gathering data. However, retrospective CPR derivation studies have made valuable contributions to many areas of medical practice.48-53 Additionally, if there had been uniformly available data across all patients, there may have been other, perhaps more powerful, predictors for treatment nonsuccess.
Actual cases of knee osteoarthritis (OA) evaluated by one of the authors (GD)
A 48-year-old female elementary teacher was referred for physical therapy due to right knee pain and a diagnosis of OA that was limiting her ability to climb stairs and squat to work with children in the classroom. Her goals were to be able to perform these physical activities with less pain and to reduce her anti-inflammatory medications. However, she also worried about taking time away from her job to attend physical therapy appointments. She was 1.63 m (5’4”) tall and had a body mass index of 27.5 kg/m2. Her knee was stable to ligamentous testing, with mild limitation and pain with active and passive movement of both the tibiofemoral and the patellofemoral joints. She had weakness of the quadriceps and hip abductors, and moderate tightness of the calf muscles in both lower extremities.
Given the presence of only a single predictor for nonsuccess (pain with passive movement of her patella), the likelihood that this patient would not respond to manual physical therapy and exercise was just 27%, according to the clinical prediction rule. The impairments to movement, strength, and flexibility found during the physical examination typically can be successfully addressed with manual physical therapy. Additionally, one of the patient’s goals was to reduce her medication use—a reported outcome of the clinical trials used for deriving the rule.1,2 This patient was a good candidate for the intervention, with an acceptably small chance of not achieving a clinically meaningful benefit.
A 50-year-old male soldier 1.95 m (6’5”) tall was referred for physical therapy to ameliorate chronic pain due to tricompartmental knee OA. He exhibited anterior ligamentous laxity and felt severe pain with manually performed passive patellar glides (FIGURES 1 AND 2). He also had a rotator cuff tear and a mild traumatic brain injury from a roadside bomb blast. With 3/3 predictors for failure, the likelihood of reducing this patient’s knee symptoms with manual therapy and exercise was just 20%. The physical therapist and referring physician jointly decided to focus a small number of physical therapy visits on the patient’s shoulder, while giving rehabilitation priority to ongoing cognitive therapy appointments.
FIGURE 1
Lachman test
With the patient’s knee flexed at 30°, draw the proximal tibia anteriorly to observe movement of the tibia relative to the femur and thereby gauge anterior cruciate ligament integrity. Laxity is suggested by increased movement relative to the opposite knee.
FIGURE 2
Passive patellofemoral glide
With the patient’s knee slightly flexed, apply light pressure to the medial border of the patella, moving it laterally and taking care not to compress the patella. Repeat the procedure superiorly, inferiorly, and medially. A positive test is pain experienced with any of the glides.
