Knee osteoarthritis prognosis

The prognosis for patients with knee OA depends on multiple factors.  Early OA may be relatively asymptomatic and patients may be able to participate in most if not all normal daily activities including sport and exercise.  It is sensible to avoid high impact activities including distance running and heavy manual work but most activities including most military activities would not be contra-indicated.  Obesity is the most important risk factor for progression that is modifiable.  Unstable knees with early OA are at risk of progression and where possible, stabilising procedures should be considered such as ligament reconstruction. Osteotomy may be an option in the knee with significant valgus or varus malalignment.

Once the cartilage damage has involved substantial areas of the joint, increasing levels of disability are expected.  Patello-femoral OA in particular affects the flexed knee, so squatting, climbing stairs and hills, and kneeling may all become substantially impaired while walking on flat ground may be less affected. While a link between the degree of radiographic OA and the degree of impairment is expected this is not always seen in practice.  It is important to consider other factors in the presentation particularly when radiographic changes are minimal and the symptoms described are of a substantial impairment.

Early prognosis. Knee osteoarthritis is a progressive condition. Obesity and joint injury appear to be the strongest risk factors that are modifiable.  The course of functional decline is generally one of stability or slowly deteriorating function, but on an individual level many patients maintain function or improve during the first three years of follow-up. Obesity is a modifiable risk factor that is also a predictor of functional decline. Physical activity has a substantial protective impact on future osteoarthritis-related disability (Suri et al., 2012).

Osteochondral allograft transplantation is of limited effectiveness in returning patients to physically demanding roles. A retrospective review was conducted on 38 consecutive allograft procedures on military personnel. The main lesion size was 487 +/- 178mm2  and the overall return to full duty rate was 28.9% with an additional 28.9% able to return to modified duties. Only 5.3% were able to return to pre-injury level of sport. When adjusted for concomitant procedures, 33.3% returned to full duty, 22.3% to limited activity and 44.4% were unable to return to duty. 7.4% were able to return to a preinjury level of sport. Marine Corps and Navy were more likely to return to full duty than Army and Air Force members, and combat arms personnel were less likely to return to full active duty (Shaha et al., 2013).

Factors associated with progression. A systematic review of adults with established knee OA looked at changes in pain, function or deterioration in radiographic features, with a minimum one-year follow-up. Thirty studies were included, of which 26 were high quality. Age, varus knee alignment, presence of OA in multiple joints and radiographic features showed strong evidence as predictors of knee OA progression. Body mass index was a strong predictor for long-term progression greater than three years. Moderate participation in physical activity was not associated with progression (Chapple et al., 2011).

Progression rates. A UK study followed 99 men and 255 women aged ≥55 years for a mean follow-up of 5.1 years with repeat radiographs. Risk factors were tested for association with incident and progressive radiographic knee OA.  Rates of incidence and progression were 2.5% and 3.6% per year respectively. Increased risk of incident radiographic knee OA was significantly increased with higher BMI , OR of OA for highest third BMI compared to lowest third was 18.3 (95%CI 5.1-65.1), previous knee injury OR 4.8 (95% CI 1.0-24.1) and history of regular sports participation OR 3.2 (95% CI 1.1-9.1). Knee pain at baseline and Heberden’s nodes were weakly associated with progression.  Overall, most risk factors influenced incidence more than radiographic progression. While incidence appears to be mostly related to mechanical injury and stress, progression appears to be a consequence of impaired intrinsic repair capacity.  As a result while knee OA is common in older people, far fewer progress to joint replacement (Cooper et al., 2000).

 The ultimate treatment for most patients with severe knee OA is unicompartmental or total joint arthroplasty.  Many patients have an excellent prognosis after arthroplasty including returning to sport and heavy manual work.  These procedures may preclude kneeling, and heavy impact activities may accelerate wear and produce early failure. Most specialists will advise against high impact or high intensity sports and heavy manual work although there is no strong evidence base to support this in all patients. Implant failure may be more related to particle-induced aseptic loosening and malpositioning than to post-operative activity.  There is some evidence that surfaces with better wear rates may be more susceptible to surface destruction with high impact activity. Choice of implant and the skill of the surgeon may therefore be the main factors in arthroplasty failure.

Function after arthroplasty. After total knee arthroplasty walking speeds for men were 13% slower at normal speed and 17% slower at faster speed.  Stair climbing was 51% slower.  Men with TKA were 37% to 39% weaker and performed 36% to 37% less total work of knee extensors compared to controls.  Women with TKA were 28% to 29% weaker and performed 24% less work (Walsh et al., 1998).

Participation in sport or activity after arthroplasty. Follow up of 88 patients showed 24% regularly participated in activities such as tennis, skiing, bicycling, or strenuous farm or construction work. Overall arthroplasty survival was 94% at 18 years although 4% of these had patellar revisions and 3% had exchange of spacer (Diduch et al., 1997).

Unicompartmental knee arthroplasty (UKA) does better than total knee arthroplasty (TKA) in return to low impact sport.  One hundred and ten patients were surveyed by questionnaire. Seventy-six patients had undergone TKA and 34 patients had undergone UKA. They were assessed for their participation in low-impact sport preoperatively and two years postoperatively. Before surgery, 55 of 76 patients in the TKA group participated in an average of 1.3 different sports and postoperatively, 35 of 76 patients participated in an average of 0.7 different sports. In the UKA group, 30 of 34 patients participated in an average of 1.5 different sports preoperatively and postoperatively, 29 of 34 patients participated in an average of 1.4 different sports. The return to sport rate was 96.7% in the UKA group and 63.6% in the TKA group. In the TKA group, the average frequency of sport preoperatively was 3.0 sessions per week (62.7 min) and postoperatively it decreased to 2.0 sessions per week (37.5 minutes). In the UKA group, the average frequency of sport preoperatively was 3.2 sessions per week (85.0 min) and postoperatively it increased to 3.4 sessions per week (92.1 min). The average time before resuming sport after surgery was 4.1 months in the TKA group and 3.6 months in the UKA group; 42.9% of patients in the TKA group and 24.1% of patients in the UKA group reported pain during sports after surgery; 80.3% of the patients in the TKA group and 88.2% of the patients in the UKA group felt that surgery had increased or maintained their sporting ability (Hopper and Leach, 2008).

High inlay stress may occur with the danger of delamination and polyethylene destruction. A literature review of current recommendations for sports after total joint arthroplasty noted that since load will influence the amount of wear exponentially, only activities with low joint loads such as swimming, cycling or possibly power walking should be recommended. If an activity is carried out on a low intensity and therefore recreational base, activities with higher joint loads such as skiing or hiking can also be performed. It is unwise to start technically demanding activities after total joint replacement, as the joint loads and the risk for injuries are generally higher for these activities in unskilled individuals. To recommend suitable physical activities after total knee replacement, it is important to consider both the load and the knee flexion angle of the peak load. During activities such as hiking or jogging, high joint loads occur between 40 and 60 degrees of knee flexion where many knee designs are not conforming and high polyethylene inlay stress will occur. Regular jogging or hiking produces high inlay stress with the danger of delamination and polyethylene destruction for most current total knee prostheses (Kuster, 2002).

Most patients can return to low impact sports, few return to high impact sports and higher impact sports are only recommended for those with past experience. Return to athletic activity after total knee arthroplasty is less viable than after total hip arthroplasty.  Most can return to low impact activities such as walking and cycling, but few return to high impact activities such as jogging and racquet sports.  Patient weight is a significant factor in high wear rates.  Highly cross-linked polyethylene has shown low wear rates but an increased fracture risk compared with conventional polyethylene. Ceramic bearings have excellent wear rates without the risk of metal ions but there have been reports of catastrophic failure on high impact loading during athletic participation. The American Knee Society produced guidelines after their 1999 Survey for activities allowed, allowed with experience and not recommended following total knee arthroplasty.  Activities allowed with experience included road cycling, rowing, cross-country skiing, tennis and weight machines.  Jogging, ball and raquet sports were not recommended  (Golant et al., 2010).  More detailed guidance can be found in the reference which is open-access.

Longevity of total knee arthroplasty in young, active patients. 82.5% of tibial and femoral components and 70.1% of all components survived thirty years. One hundred and eight knees were followed up and a significant difference was noted between the non-modular Insall-Burstein 1 componentn (92.3% survival) and the modular Insall-Burstein II component (68.3%) (P=0.003) (Long et al., 2014).

A review of worldwide National Joint Registries undertaken in 2014 showed the current risk of failure of TKA requiring revision surgery ten years post-operatively is 5%. The most common indications for revision include aseptic loosening (29.8%), infection (14.8%) and pain (9.5%) (Khan et al., 2016).

Ability to kneel after knee arthroplasty. A major limitation following knee arthroplasty is inability to kneel.  There have been a number of studies looking at patients’ ability to kneel with varying results.  Most indicate that significant numbers (up to 80%) of patients have a perceived inability to kneel but observations show that provided there is sufficient range of movement most patients can kneel after arthroplasty. Surgeons often advise against kneeling because of theoretical risk of damage to joint components but there is no clear evidence-base to support this.  Kneeling is an important function of daily activity and there is no evidence to discourage kneeling where patients can do so and are comfortable doing so.  It may be appropriate to advise them to avoid repeated kneeling, avoid undertaking heavy manual activity while kneeling, and avoid moving around on their knees on hard uneven surfaces. (Clement et al., 2015, Hassaballa et al., 2007, Hassaballa et al., 2004, Hassaballa et al., 2003, Jenkins et al., 2008, Palmer et al., 2002, Schai et al., 1999, Sofat et al., 2006)

Kneeling is possible after total knee arthroplasty. Range of motion, loading, contact and kinematic studies showed that kneeling may be performed where postoperative knee range of motion is greater than 120o, and there is less risk to the patellofemoral joint than previously believed. Increases in tibiofemoral contact area and pressures may lead to polyethylene wear if performed on a chronic repetitive basis (Lee, 2014).



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