Musculoskeletal Disorders: Knee
Appendix A: Overview of Medical Evaluation of Knee Disorders
Separating individual anatomical structure and/or individual knee injuries has been a long-standing diagnostic and research challenge. In most research settings, subjects are excluded with concomitant injuries in order to evaluate a specific surgical technique or intervention. In reality, most knee injuries are not isolated to one specific area. A relevant example is the well-known “unhappy triad” – rupture of the medial collateral ligament, damage to the medial meniscus, and rupture of the anterior cruciate ligament. Peer-reviewed studies give a framework for functional outcomes and/or return to activities; however, it is unlikely that the LEO with a knee disorder will fit neatly into the peer-reviewed literature.
The consensus of the Task Group is that there is commonality in the post-injury evaluation and management of acute and chronic knee injuries. The police physician should be able to make an objective determination of the LEO’s ability to perform essential job functions regardless of the type of acute or chronic knee injury (total knee arthropathy is discussed separately). See Appendix D for examples of physical essential job functions from other sources.
The peer-reviewed literature contains articles on return to play/participation following knee injuries in various cohorts. Cohorts include high school and college athletes, U.S. and international populations, U.S. military and service academies, and professional athletes. This suggests that, in many cases, the LEO who has recovered from an acute knee disorder will be able to perform their physical essential job functions (running, squatting, crawling, up/down stairs, jumping) in the same fashion that an athlete returns to practice and competition. In both cases, the athlete and the LEO have been cleared by their musculoskeletal provider to return to the activity in question, presumably based on objective physical findings, post-injury rehabilitation timing and pathways, and the individual’s desire to return to that activity. Therefore, there should be minimal differences in assessing the physical ability to return to play for an athlete and return to unrestricted duty for the LEO.
- Range of motion – There are several methods to assess flexion and extension of the knee including visual estimation, hand goniometry, and radiographic goniometry.1 No one method is better than the other and all methods will evaluate flexion contractures (i.e., lack of full extension) and decreased flexion for the purposes of documenting “normal” knee range of motion. Knee flexion in the stance phase of gait allows for an average of 15° of knee flexion to allow the foot to become flat on the ground. Inability of the knee to participate in locomotion comes at increased energy costs,2 so documentation of functional knee range of motion is important. Functional flexion of the knee is usually defined as ≥90° of flexion as this allows for ambulation, ascending/descending stairs, and ability to sit in most community settings (taxi, church, airplane, etc.). In assessing function for any knee disorder, it is reasonable to require and document both active and passive range of motion on the knee in extension and flexion. If there are only minimal losses (i.e., no more than 5° loss of extension and ability to achieve at least 90° of flexion), the subject can be assumed to have adequate range of motion for almost all tasks, the exception being a deep squat (assessed separately), with good reliability and safety assuming the patient has been cleared by their provider for return to activity (footnote: full depth squatting loads the meniscus and is usually the last task achieved post-operatively). Given the importance of the knee to locomotion, loss of knee range of motion is readily apparent in gait analysis. If a subject can walk without a limp (assuming other gait determinants are within normal limits) with the knee disorder, the examiner can move on to the next set of criteria.
- Strength – Quadriceps, hamstring, and gastrocnemius are all involved in the functional strength of the knee. Body weight testing (i.e. having the LEO plantar flex while standing to test gastrocnemius) and/or functional testing (i.e. getting up and down from a chair or ascending/descending stairs to test hamstring and quadriceps) is preferred given the strength of the knee extensors and flexors. Weak gastrocnemius causes ankle and knee flexion during testing. Weak quadriceps is compensated for by thrusting the knee into hyperextension.3 Comparison with the other limb should be done and documented.
- Pain – Significant pain with activities may or may not be a limiting factor to the LEO with a knee disorder. Pain that is vague or intermittent is a common human condition and should not disqualify an individual. If an individual reports knee pain, but is able to jump, run, crawl, walk, up/down stairs, it is unlikely that their baseline pain puts them at higher risk for sudden incapacitation. The police physician should document use of any pain medications.
- Function – Despite the numerous and various injuries and surgical techniques for knee disorders, the assessment of recovery relies on only a few, validated assessment tools, the most common of which are the SANE, Lysholm (symptom-based) and Tegner (activity-based) scales (see Appendix C). Normative age and gender data is available, with Tegner activity level decreasing with increased age. These tools are easy to administer, short in length, and have been validated for a variety of knee conditions, including ligament injuries, chondral disorders, meniscal injuries, and patellar dislocation.4,5
- Objective laxity – Knee laxity may interfere with cutting, pivoting, rapidly ascending and descending stairs (see job simulation tasks in number 11 below). Knee laxity is relative. Truly objective ligament testing is only available in research settings.6 Return to unrestricted duty will require functional assessment to ensure adequate performance of essential job functions.
Proposed Assessment for Medical Clearance for any Knee Disorder:
- Documentation of initial injury/disorder including any concomitant injuries to same-side hip and ankle.
- Documentation of clinical evaluation (including imaging) that led to the diagnosis.
- Timeframe from initial injury to current evaluation – most if not all rehabilitation pathways are time-dependent for increasing activities.
- Documentation of treatment of injury (operative vs. non-operative).
- Pain medication, brace, other modalities used for knee disorder.
- Objective data – knee range of motion, deep squat (the hip drops below the level of the knee), gait, laxity, instability, effusion, quadriceps diameter (muscle atrophy), and quadriceps, hamstring, and soleus strength. Assessment should include both knees.
- Pain with activities should be noted.
- Documentation of physical activity level since the treatment of the injury.
- Documentation of any instances where the affected knee has given way during sports and/or vigorous activity. Document any activities that the LEO has avoided since injuring the knee.
- Kozlowki, et al, suggest the following criteria be achieved before initiating a return-to-sport phase: Lysholm score >75 (see Appendix F), SANE score >75 (see Appendix F), normal performance of activities of daily living, no effusion of the knee, full range of motion, and quadriceps muscle atrophy <2 cm when compared with opposite limb. Strength testing parameters include single-leg press >70% of normal (using the uninvolved side as a reference), knee extension/flexion >70% of normal, single-leg squat >60°.7 Note that these criteria are proposed to allow an athlete to being the training phase of their sports-specific activity. These are not criteria for return to unrestricted duty.
- If the police physician is concerned with the LEO’s ability to return to unrestricted duty, the following job simulation tasks may be used as part of the return-to-work decision making: defensive tactics, running (especially short-burst running on uneven terrain), climbing over obstacles, ascending/descending stairs and ladders, entering and exiting from a vehicle, kneeling, squatting, jumping (especially jumping down from a height) and prolonged walking and standing.
- Before returning to unrestricted duties, the police physician should document that the LEO has successfully returned to physical training, which includes the tasks described in item #11. The LEO must be evaluated on an individual basis and assessed by tools such as job simulation tasks and/or physical training activities in order to objectively document an individual’s ability to return to a higher-level demand job such as law enforcement.