Musculoskeletal Disorders: Knee

Appendix B: Discussion of Knee Disorders

A. ACL Injuries
Anterior cruciate ligament (ACL) injuries are common in the U.S., with estimates of 80,000-100,000 repairs performed each year.8 Highlights of some recent publications are presented below:

• Sports trauma related to basketball, judo, wrestling, and track and field were found to be the activities associated with ACL injuries.9 Of the 4,355 patients with ACL injury (athletes and non-athletes), 89.7% went on to surgery.
• In a study of 617 ACL injuries collected from 100 U.S. high schools, injuries were more common in competition than practice (RR = 7.3 [6.08, 8.68]). Girls’ soccer had the highest injury rate, followed by boy’s football. In sex-comparable sports, girls had a higher rate of injuries compared to boys (RR = 3.4 [2.64, 4.47]); 76.6% of ACL injuries resulted in surgery.10
• 506 female basketball athletes who participated in the combine for Women’s National Basketball Association from 2000-2008 had a 15.0% incidence of ACL injury with 14.4% having ACL reconstruction. History of ACL or meniscus surgery did not affect career length in the WNBA.11

There are several studies in military populations on ACL injuries and successful return to unrestricted duty. In a study of 111 Malaysian military patients, 82% of ACL injuries were due to sporting activities. Follow-up at 1 year showed that almost all patients resumed prior activities, although 40% were lost to follow-up.12 In 169 primary ACL cases performed on active-duty military (special operations force), 155 (92%) were able to return to full duty by 7.3 months (+/-2.3 months).13 In a study of 112 ACL reconstructions in cadets at the U.S. Military Academy who presented with an ACL reconstruction at the time of matriculation, there were 20 failures over time (mean time to failure 1.5 years), with allografts more likely to fail compare to autologous graft reconstruction (p <0.001).14

At the time of this writing, ACL repair is recommended for patients who desire to resume high-intensity activity and/or are experiencing recurrent episodes of giving way.8 A recent meta-analysis of operative versus non-operative ACL management in pediatric patients reported that no patients treated non-operatively were able to return to their prior level of sport.15 It is important to document the details surrounding the injury as isolated ACL injuries (non-contact caused by cutting/pivoting as the quadriceps decelerates) are thought to do better post-repair compared to ACL injuries by contact (often with resulting cartilage/other ligament/meniscal damage). The consensus of the LEO Task Group is that, although surgical repair is more likely to result in return to pre-injury function, it is possible for a person without surgical repair or with ACL deficiency to be able to return to unrestricted duty.

A 2011 review and meta-analysis of 5,770 patients who underwent ACL surgery (54% male, mean age at follow-up 25 years old [range 13 to 60 years], mean follow-up 41.5 months [range 12-85 months]) showed the following:16

• Graft type: patellar tendon graft (69%); hamstring tendon graft (20%)
• Return to sport (any): pooled analysis 82% (95% CI 73-90%)
• Return to sport (pre-injury level): pooled analysis 63% (95%CI 54-71%)
• Return to competitive sport: pooled analysis 44% (95% CI 34-56%)
• Duration to return to competitive sport: mean 36.7 months
• Comparing pre-2000 studies with post-2000 studies: return to competitive sport was 44% pre-2000 and 56% post-2000 (p <0.001)

While a discussion of surgical preference (allograft vs. autograft, patellar tendon vs. hamstring tendon) is beyond the scope of this document, the published research suggests that there are factors besides anatomical and rehabilitation outcomes (e.g., desire to play, fear of re-injury, or loss of starting position) that influence return to play after ACL injury and/or repair. There is also a wide range of successful return to work/play reported between published studies in military personnel (high rate of return to duty) and general population studies (less than half returning to prior competitive sports). Additionally, while most day-to-day physical essential job functions of the LEO should be performed without risk of sudden incapacitation, some training activities are likely to be compromised in all but the best clinical outcomes.

The police physician should also be aware that ACL injuries are often associated with other ligament and cartilage injuries and most research has excluded this population from study. In one large ACL registry, meniscal repair at the time of index ACL repair was associated with a four-fold re-operative rate, compared with ACL repair without meniscal repair. The overall re-operative rate was 2.7 per hundred person-years.17

B. Collateral Ligament Injuries
Medial collateral ligaments (MCL) injuries are graded from Grade 1 to Grade 3 based on medial knee opening with valgus stress.18 In a cohort of U.S. Army cadets, Grade 1 injuries were returned to activities within 2 weeks, Grade 2 and 3 injuries required 4 weeks for return to activities.19 Return to play after lateral collateral ligament injuries is similar to MCL injuries (23 days +/-26 days versus 23 days +/-23 days).20 In this elite athlete cohort, posterior cruciate ligament injuries also returned to play much sooner than ACL injuries (52 days +/ 57 days versus 194 days +/-75 days.20

In contrast to ACL injuries, the vast majority of isolated collateral ligament injuries are treated non-operatively. It is important to document any subjective knee instability as well as objective ligamentous laxity difference between limbs. Reasonable guidelines on return to sports or strenuous activities after an appropriate recovery period is similar to meniscus injuries and requires a non-tender joint line, absence of pain and effusion, full range of motion (especially extension) and restored muscle strength.21

C. Meniscus Conditions
Arthroscopy of the knee is the most common orthopedic procedure performed in the U.S.22 The knee contains both a medial and lateral meniscus which serve several functions including load transmission, improving joint congruency, reducing joint contact stresses, shock absorption, providing passive stability especially in the ACL-deficient knee, and providing some lubrication and nutrition within the synovial cavity.22

Knee pain, lack of mobility, effusion, and thigh atrophy are all common findings after acute injury, as well as after conservative or operative treatment. Commonly used scales, including the Lysholm and Tegner have shown acceptable properties for documenting knee function after meniscal injury.23 Functional outcomes are usually reported by surgical technique – however, many traumatic medial meniscus injuries also have concomitant ACL injuries.24 Similar to ACL injury return to activities, reasonable guidelines on return to sports or strenuous activities requires a non-tender joint line, absence of pain and effusion, full range of motion (especially extension) and restored muscle strength.21

At the time of this writing, surgery is usually recommended for unstable or symptomatic meniscal tears (displaced meniscal fragment on MRI and/or a positive McMurray test on exam).25 There have been several recent randomized trials on the role of surgical repair of meniscal tears in the setting on osteoarthritis of the knee.26,27 These studies have shown no difference between operative and non-operative management of meniscal tears at 6 months and 2 years. Of note, large “bucket-handle” tears and patients who experience frequent locking of the knee are typically excluded from these studies. Recovery time from surgery to return to sports is typically 5 to 6 months, longer if there are other concomitant injuries. It is the consensus of the Task Group that, although surgical repair of unstable meniscal tears is more likely to result in return to pre-injury function, it is possible for a person without surgical repair to be able to return to unrestricted duty. Stable asymptomatic meniscal tears do not require surgery.

D. Knee Replacement (Arthroplasty)
Osteoarthritis is the most common indication for knee replacement, accounting for almost 90% of knee replacement surgeries.28 Less than 20% of knee replacements occur in persons under age 65; however, the percentage of persons aged 55 to 64 undergoing a knee replacement has increased by 50% over the past 20 years.29 Persons aged <55 had a 10-year survivorship of 83% (79-86%) for their initial knee replacement, with outcomes worse for persons with diagnosis of post-traumatic arthritis and osteonecrosis.29 In a multivariate model of 11,608 primary total primary knee arthroplasties from Mayo Clinic from 1978 to 2000, younger age, male gender, implant type, diagnosis, uncemented fixation, and patellar design were all associated with higher risk of revision.28

The National Fire Protection Association’s criteria for medical clearance after knee replacement is as follows30:

• Normal range of motion without history of dislocation post-replacement;
• Repetitive and prolonged pulling, bending, rotations, kneeling, crawling, and climbing without pain of impairment;
• No limiting pain;
• Evaluation by orthopedic specialist who agrees that the candidate can complete all essential job tasks.

Realistic return to activity expectations for patients undergoing total knee arthroplasty (TKA) have traditionally focused on lower impact activities, such as walking, use of an elliptical trainer, swimming, golf, light hiking and biking. This rationale is based on the theoretical acceleration in polyethylene wear and earlier eventual failure of the TKA. However, some patients will return to high-impact activities after TKA and the limited published outcomes demonstrate that participation does not cause radiographic evidence of wear (note: majority of persons participated in singles tennis, high-impact aerobics, and jogging).31 While the occupational and training tasks required of the LEO have the potential to accelerate prosthetic wear, the Task Group does not specifically recommend increased radiographic screening to detect early prosthetic failure in asymptomatic individuals. However, the LEO should make his/her surgeon aware of the current level of physical activity.

Examination of the surgically repaired knee after TKA does not differ greatly from other knee conditions. The police physician should document a well-healed scar, any varus/valgus deformity in stance, and normal quadriceps strength. Examination of the opposite knee should also be done as conditions leading to TKA are often bilateral. The most common functional outcome scale after TKA is the Knee Society Scoring System. The same scoring system is used in the pre-operative and post-operative setting and includes both an objective functional evaluation (stability: medial, lateral, anterior, posterior; range of motion; and symptoms) and a satisfaction score. It is noteworthy that the satisfaction scores are skewed towards improvement with lower-level activities (pain level while sitting, getting out of bed, performed light household duties) with minimal scoring for advanced and/or sports activities. Due to the increase in activity levels in the TKA population, a new Knee Society Scoring System was introduced in 2011.32 Of note, the 2011 Knee Scoring System has four sub-scales: climbing a ladder or step stool, carrying a shopping bag for a block, squatting, kneeling and running. The LEO would be expected to score highly on the Advanced Activities sub-scale.

E. Bilateral and Revision TKA
It is the Task Group’s consensus opinion that the LEO who has either a revision TKA of a unilateral joint or bilateral TKA is likely to need restrictions.33 Revision TKA has lower success rates compared to primary TKA, as well as higher rates of complications.34 Prolonged knee complications are likely to affect quadriceps strength and functional ability. Job task simulations are recommended after revision TKA to document the LEO’s ability to perform their physical essential job functions. Outcomes after bilateral TKA have been difficult to study, in part because of the difficulty of the patient separating out the contributions of the individual knees to their functional outcomes. There is some evidence that persons with bilateral knee replacements have better outcomes compared to unilateral knee replacements with ongoing contralateral knee pain.35,36 However, the underlying process leading to the need for bilateral knee replacement makes it likely that the LEO will require restrictions.

F. Prediction of Future Disability/Arthritis

It is well established that prior injury may lead to earlier functional decline of the affected joint. A recent review comparing non-operative to operative management of ACL injuries (follow-up at mean of 12 years) did not show any difference in Tegner or Lysholm scores or radiographic evidence of arthritis between the two groups.37 However, both groups needed knee surgery (12.4% of operative group versus 24.9% of non-operative group) during the observation period. In the previously described cohort of U.S. service cadets, roughly 20% of cadets who presented freshman year with prior ACL injuries needed to undergo additional surgery on the affected knee.14 The Task Group is unable to suggest a valid methodology for predicting future disability and/or timeline for progression of disability after knee injury. This is in part due to the multi-factorial nature of knee injuries, ever-changing operative and rehabilitation strategies, and non-modifiable risk factors such as age and gender. Treating physicians may make recommendations on physical activity to prevent future deterioration of the involved joint. This is particularly true with weight-bearing joints (hips, knees, ankles). Future joint deterioration/degeneration should not be taken into consideration when performing fitness-for-duty evaluations on LEOs with knee conditions.

G. Temporary and Permanent Knee Braces
It is the LEO Task Force’s consensus opinion that knee braces in good working order are acceptable for LEO use on-duty provided the same or similar brace is used during qualification and training activities (Note: this does not include post-operative protective knee braces). If knee brace use is intermittent, the LEO should be able to perform the physical essential job functions both with and without the brace. The LEO who requires a brace in order to perform the physical essential job functions is required to wear the brace at all times when on duty.