The influence of quadriceps strength on knee cartilage
A significant negative association between baseline quadriceps force and cartilage damage, change in BMLs and effusion synovitis was found in women, but not in men
This confirms the protective role of the quadriceps muscle for knee health
The results were based on data from an open register, and valuable information is lacking
Introduction
Optimal quadriceps strength is essential for good knee function in daily life. As the quadriceps muscle is an important stabilizer and shock absorber, it helps distribute loads on the articular surface of the knee. This is very important, especially in the light of an aging population and increasing numbers of people with obesity. As there is currently no real cure for knee osteoarthritis (OA), it is crucial to slow down the progression to OA or – when possible – prevent the onset of it. Therefore, strengthening has been advocated as the first-line treatment for knee OA. Up till now, firm conclusions could not be drawn for the influence of quadriceps strength on knee cartilage. That’s where this study kicks in.
Methods
In this multicentric prospective cohort study 1338 participants were included who provided data of 1505 knees. At the one-year follow-up, 1225 participants were available, providing data for 1366 knees. Besides the demographic data, the radiological severity of knee OA was recorded using the Kellgren-Lawrence scale from 0-4 (none to severe).
Knee strength was measured using the “Good Strength Chair”, which has been reported to be a valid and reliable measure. Here participants were seated upright with their thighs and pelvis fixed and the knee in 60° of flexion. After an initial attempt trial, 3 voluntary maximal isometric efforts were completed. The highest attempt was used for the analyses.
MRI data was also collected at baseline and follow-up. Cartilage damage was assessed in the medial and lateral tibiofemoral complex (M- and LTF), and in the medial and lateral patellofemoral joint (M- and LPF). Damage was rated as follows: 0=normal, 1=small (<10% area damaged), 2=medium (10–75% area damaged) and 3=large (>75% area damaged). Cumulative scores were calculated for the MTF, LTF, MPF, and LPF joints. In the MTF and LTF these cumulative scores ranged from 0-15 and in the MPF and LPF joint, the cumulative scores ranged from 0-6. Next to this, bone marrow lesions (BML) were rated from 0-3, where scores represent: 0=normal, 1=small (<33% area damaged), 2=medium (33–66% area damaged), and 3=large (> 66% area damaged). Here also cumulative scores were calculated.
Effusion-synovitis was graded from 0 to 3 in terms of the estimated maximum distention of the synovial cavity as follows: 0 = normal, 1 = small (< 33% maximum distention), 2=medium (33–66% maximum distention), and 3=large (>66% maximum distention). The same classification was used to rate the extent of Hoffa synovitis in terms of the estimated hyperintensity alteration area within the infrapatellar fat pad.
Results
The results show that considering knee cartilage damage in males at baseline, there was an influence of quadriceps strength on cartilage damage in the LTF and LPF compartments. However, no significant change in cartilage damage was observed at 1 year. At baseline, as was seen in men, cartilage scores of the MPF and LPF were significantly associated with quadriceps strength. After 1 year, a significant negative association was observed between quadriceps strength and worsening cartilage damage in females.
Considering BMLs, at baseline an association was found between quadriceps strength and BMLs in the LTF compartment in men, and in the MPF and LPF compartment in women. Over the course of 1 year, only in the LPF compartment in females, a significant negative association was observed.
The synovitis scores revealed that at baseline in women, quadriceps strength was associated with Hoffa-synovitis. After the follow-up of one year, it appears that baseline quadriceps strength was associated with effusion-synovitis.
Questions and thoughts
Importantly, most of the participants from this population were overweight, having a BMI of 29.4 +/- 4.7kg/m2. Findings were adjusted for BMI, but unfortunately, no details on this were provided. Also, no information was provided for changes in BMI throughout the course of the study. This would have been interesting to analyze as well, as it is a modifiable parameter, just as quadriceps strength is. This study used data from the Osteoarthritis Initiative, which is a publicly available database. To me, it seems that the authors were thus not in contact with the participants directly, which could explain the lack of additional information for example on sports participation.
Next to this, it would have been valuable to have insight in the cartilage scores at follow-up. The baseline scores were presented in a table, but we cannot see the progression of these scores at follow-up. We have no clue about the influence of injuries, which could result in effusion or cartilage/BML damage. Also, force output could have been influenced by pain, and again, this information was not available. It appears that we miss a lot of valuable information, unfortunately. We only know something about the change in cartilage damage, BML, and effusion after one year. But we cannot make assumptions about what has driven this change over the study period. Registry-based studies can be very insightful but often lack valuable clinical information.
In women, after one year, changes in lateral patellofemoral cartilage and BMLs were significantly associated with baseline quadriceps strength. Knowing this, and knowing that women are generally less strong than men and often have a morphological predisposition to greater lateral patellofemoral forces than men, this underscores the tremendous importance of improving quadriceps strength in women to protect their knees. So be sure to correct for adaptable postural alignment and maltracking issues and improve quadriceps force!
Talk nerdy to me
Some findings of this study were analyzed cross-sectionally, meaning that they were evaluated at one specific point in time. For example in males at baseline, an association was found between quadriceps strength and cartilage damage in the lateral tibiofemoral and lateral patellofemoral joint. When looking at the longitudinal analysis, no change in cartilage damage was observed. Remember that cross-sectional analyses only give information about data at one specific time point. It is thus not possible to use the findings of such an analysis to establish cause-effect relationships. Furthermore, the timing may have a huge impact on the findings. Let’s say that an important part of these participants had participated in a long-distance running event prior to the baseline measurements of this study, this could have caused transient post-exercise changes to their cartilage, as captured here at baseline. Just an example to explain why we should not rely too heavily on findings from cross-sectional studies. I rather suggest looking at the longitudinal data, especially as we see that the significant findings at baseline were not necessarily significantly changed over the course of the study period.
The authors corrected the findings for age, BMI, race, Kellgren-Lawrence grade, injury, surgery, and structural abnormalities at baseline. Thus, as can be seen, no information was available on activities performed prior to assessment at baseline, nor, for example, participation in sports. Therefore, no information on potentially influencing factors is available to frame the findings of the cross-sectional analyses. Last but not least, the authors stratified the analyses by sex, which is a good option as women tend to have lower strength than men.
Take home messages
To recap, the influence of quadriceps strength on cartilage damage was examined here. Quadriceps strength measured at baseline was significantly and negatively associated with changes in cartilage damage, changes in knee bone marrow lesions (BMLs), and changes in effusion-synovitis in women. Both the changes in cartilage damage and BMLs were evident in the lateral patellofemoral joint in women. This means that higher quadriceps strength at baseline led to fewer changes in cartilage damage and BMLs. The lower the strength of the quads at baseline, the more damage to the cartilage and bone marrow was observed. Even in this short period of time, significant worsening of cartilage and subchondral bone parameters are observed in subjects with low quadriceps force. This again confirms the protective role of the quadriceps.
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