Meniscectomy is a risk factor for osteoarthritis (OA) of the knee (1–6). We have shown a 6-fold increased relative risk for development of radiographic OA after total meniscectomy, compared with unoperated controls (7, 8). Variations in disease prevalence between studies on this topic are likely due to heterogeneity of patient groups, high dropout rates, and varying classifications of radiographic OA (9). The contributions of and interaction between different risk factors for OA of the knee after meniscectomy are similarly difficult to evaluate and sometimes contradictory, probably owing to the same reasons, as well as to the absence of multivariate analysis (2, 3, 5, 6, 10). In addition, most outcome studies of meniscectomy are compromised because patient-relevant outcome instruments are not used, thus increasing the risk for introduction of bias by the interviewer (11, 12).
We have previously demonstrated an interaction between the endogenous risk factor heritable OA and exogenous OA risk in the form of meniscectomy (13), as well as the impact of the type of meniscal tear that may indicate preexisting early-stage knee OA (8). The present study was undertaken to evaluate the influence of additional risk factors for OA in the meniscectomized knee. We specifically evaluated the effect of age, sex, body mass index (BMI), arthroscopic or open surgical technique, extent of meniscal resection, intraoperative cartilage changes, and knee load during work and leisure on the development of radiographic OA and symptoms in the operated knee. We studied a well-defined and carefully characterized cohort, using a combination of validated self-administered questionnaires and standardized radiographic procedures.
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- PATIENTS AND METHODS
Knee injury is an important risk factor for knee OA (20–22), but little is known of the mechanisms leading to osteoarthritic disease in the injured joint, or how injury interacts with other risk factors. In this study we investigated a well-defined and carefully characterized cohort of 317 subjects who had undergone meniscal resection 15–22 years previously. Among all patients who had undergone this procedure, the loss to followup was low.
Knee OA after meniscectomy is traditionally considered a result of joint injury and increased cartilage contact stress due to the loss of meniscal tissue (23). “Wear and tear” is a straightforward explanation for OA, and surgery in which an intact peripheral rim of the meniscus is preserved would thus be expected to produce better long-term results. If there is a substantial intact portion of the circumferentially oriented matrix fibers, hoop tension, which counteracts meniscal extrusion when the knee is loaded, may still develop. Substantial function of the residual meniscus in shock absorption and load transmission would thus remain.
However, the evidence for improved long-term outcome after partial meniscal resection is limited (2, 8, 24–26). To our knowledge, the present study is the first, using a large number of subjects, to show that partial meniscal resection induces less radiographic OA over time than does total meniscectomy. The frequency of subjects experiencing symptoms was not substantially reduced, however. Although, the statistical power in our sample for detecting smaller proportional differences in numbers of symptomatic subjects was low, the raw KOOS data (not shown) supported our finding of a very limited effect of resection size on the patient-relevant outcome. Therefore, in view of the present and previous results, evidence for a greatly improved long-term patient-relevant outcome with the use of partial meniscectomy still appears weak.
Obesity is an established risk factor for knee OA (27, 28). We cannot rule out the possibility that some subjects in our study could first have developed OA and then become sedentary and overweight. However, using retrospective estimates of weight from the patients who underwent surgery in 1973 and 1978, we did not find any evidence for such a cause and effect. Therefore, our results strongly suggest that obesity is an important risk factor for the development of knee OA also in meniscectomized subjects. Consequently, it is important to encourage weight loss in obese patients who have undergone this surgical procedure and are at very high risk of developing OA (29).
Our finding of worse radiographic outcome in association with lateral meniscectomy is consistent with other reports (3, 5, 6, 25, 30). The lateral meniscus has been reported to carry a higher load in the knee compared with the medial meniscus. Consequently, its loss may result in increased cartilage contact stress (31, 32).
In community-based studies the prevalence of knee OA steadily increases with age (33, 34). Although there was an increase in prevalence with patient age in our study, this pattern seems less evident in knees that have undergone meniscectomy. The reason may be the introduction of an additional biomechanical risk factor (the loss of meniscal function). The limited time range since surgery in the present study limited the possibility to evaluate the influence of time.
Women appear more likely to develop symptomatic OA (27), suggesting that the complex relationship between biological, physiologic, and psychosocial factors to explain knee symptoms in OA needs further attention. In our study, just over half of the patients with radiographic OA had symptomatic disease, corroborating earlier observations (35).
Even if an arthroscopic surgical technique and a limited meniscal resection were used, patients still had a high risk of developing symptomatic or asymptomatic radiographic OA. Other risk factors thus need to be addressed. The contributing influence of heredity has been suggested by the association between radiographic OA of the hand and radiographic OA of the knee found after meniscectomy (13, 36). We have previously demonstrated the impact of preexisting early-stage OA (8); in further support of this is the higher frequency of intraoperative cartilage changes seen in conjunction with the degenerative type of meniscal tear in the present study, consistent with previous findings (37, 38). Patients with meniscal symptoms due to a degenerative tear may thus constitute a subpopulation enriched in individuals with incipient OA. However, the relationship between meniscal tears and pain is questionable (39), and in joints without specific mechanical symptoms, meniscal surgery may therefore often not be indicated. The intervention merely removes evidence of the disorder, while the OA joint degradation proceeds (40).
This was a retrospective cohort study with the limitations associated with such studies. Although the loss to followup of 30% was low compared with other studies of meniscectomy, selection bias may have occurred in both the patient group and the control group; the presence of knee symptoms among those invited could have generated a greater interest to participate. In contrast to findings in previous studies (41), our results did not reveal significant differences with respect to knee load. One explanation could be that it is difficult for patients to accurately estimate their load retrospectively. A further possible limitation of our study was that information on knee alignment, smoking history, and chondrocalcinosis was not recorded.
In conclusion, the contributing risk factors associated with the development of knee OA following meniscectomy are similar to those for knee OA in general. Systemic and local biomechanical risk factors interact. In addition to preexisting early-stage knee OA at the time of the index surgery, the demographic factors associated with the highest likelihood of symptomatic disease were obesity and female sex. When surgical repair of a symptomatic meniscal tear is not possible, a limited resection should be used, because total meniscectomy was associated with more radiographic changes of OA.