Introduction

There is no doubt about the benefit of strengthening exercise in people with osteoarthritis. Many trials and exercise programs have been established and investigated. Most of them target the quadriceps, hip abductors, and calves in the first place. It is thought that improving the force of the quads reduces knee joint loads, improves calf strength improves walking capacity, and controls Trendelenburg gait by improving the strength of the hip abductors. But what about the adductors? The authors aimed to investigate the effects of adding hip adductor strengthening to a multimodal exercise program for individuals with knee osteoarthritis (OA).

Methods

In this randomized controlled trial, patients between 50 and 80 years of age with knee OA were included. The inclusion criteria that had to be met were:

• Knee OA grade 2-4 (Kellgren-Lawrence scale)
• Minimal knee pain 3/10 on the NRS
• Pain and functional impairment in the last 3 months (how was this assessed?)
• Meeting at least one of the American College of Rheumatology criteria (knee pain, presence of osteophytes, associated with at least 1 of the following: > 50 years, morning stiffness of <30 minutes or crackling during active movement of the knee)
• Gait independence (how was this assessed?)
• No prostheses or orthoses
• Unilateral or bilateral symptoms
• Predominant pain located in the medial knee

The interventions of the double arm parallel trial consisted of a group receiving hip abductor exercises and a group performing hip adductor exercises next to a multimodal training program consisting of a warming up, stretching, tibiofemoral and patellofemoral mobilizations, and knee and calf muscle strengthening. These exercises were supervised by a physiotherapist and performed individually twice a week for 6 weeks. Each session had an average duration of 60 minutes and the exercises were performed in three sets of 8–12 repetitions and a Borg Rating of Perceived Exertion (RPE) of 60–80%.

The starting loads were chosen based on the participants’ capacity of completing 8-12 repetitions of a given exercise at a Borg intensity of 60-80%. Progressions of 2-10% were made once the participant was able to perform at least 14 repetitions in the last set or when the Borg perceived exertion was below 60%. This seems an effective progression and an easy-to-use method to implement in clinical practice. Equally, when symptoms worsened with the use of increasing loads, the number of repetitions in each set was increased to still ensure progression was made.

The primary outcome of interest was the patient-reported pain on the NRS scale and the KOOS subscales of pain and activities of daily living at the 6-week follow-up. In the case of bilateral symptomatology, the most symptomatic limb was used to assess the outcomes.

Results

In total, 66 patients were included and equally randomized to the hip adductor or hip abductor strengthening group. In both groups, there were more participating females than males. The reported treatment adherence was high with on average 10.9 (+/-1.8) in the abductor group and 10.8 (+/- 2.1) sessions in the adductor group. This difference was not significant thus both groups’ treatment adherence was considered equal.

After the 6-week program, both groups improved on the primary outcomes but no between-group difference was seen. This was similar to the secondary outcomes, where also no difference was seen between the abductor and adductor group. Also, both groups demonstrated a similar total work during the sessions. This was calculated by multiplying the number of sets, repetitions, and RPE (and load in the weighted exercises).

Within-group improvement was not examined as the trial wanted to compare the adductor to the abductor exercise group. However, upon inspection of the reported changes on the NRS, both groups achieved a pain reduction of nearly 3 points which may be considered a clinically relevant improvement. Same for the other primary outcome KOOS-pain, where an increase of approximately 20 points was achieved.

Questions and thoughts

Based on the total workload graph hereunder, visually we can see increases in total workload, reflecting an exercise progression over the weeks. The graphs for the total knee extension, flexion, triceps surae and squatting workload showed the same evolution as the graph depicted here below.

The authors in their introduction question the relevance of the improvements seen when adding hip strengthening exercises to the rehabilitation of knee OA. As the improvements seen may be linked more to an increased exercise dosage than to an effect of hip exercises, the authors wanted to compare 2 such exercise programs with equal dosage. Indeed, both groups improved and there was no difference between the abductor and adductor strengthening. Therefore, at least in this study, improvements seem to be more dose-dependent, but as no low-dose group was included, this cannot be confirmed.

The choice of adding hip adductor strengthening may seem a bit weird, but it was based upon the fact that in people with knee OA, impairments in hip adduction strength have been noted compared to healthy controls and on the association of adduction weakness and progression of knee OA.

The exercises were performed in open and closed kinetic chains and the full ROM was allowed. To facilitate the execution of the exercises, it was allowed to reduce the ROM when the pain scores exceeded 3/10. Rather than hard progression criteria, the progressions made were mediated by pain levels. Especially in older adults with no to little participation in sports/exercise, I think this may be an effective way to achieve rehabilitation goals. Rather than deterring them, this trial tried to tune the capacity of the individual to the progressions to make. Starting low and building up high may seem more achievable in their perception and this in turn may possibly influence adherence and trial completion, in my opinion. As stated also by the authors, “the perception of the practice of physical exercises in greater volume can also change the way of coping”.

The reported treatment adherence was high in both groups, so it seems that adding hip adductor strengthening was generally well tolerated and feasible. On top of that, no adverse events were reported. This may be due to the use of the Physical Activity Readiness Questionnaire, which assessed if there were any contraindications to exercise therapy before trial commencement.

Talk nerdy to me

In the statistical analysis section, it was mentioned that the Shapiro-Wilk test was used to check the normality of the data distribution. However, nowhere in the article, the results of this analysis were reported. Upon visual inspection, it seems that both groups are comparable at baseline.

This RCT corresponds to several trial requirements such as an effective blinding of the assessors, prospective registration, sample size calculation performed a prior, and randomization by a researcher not involved in the collection of data. The physiotherapists were trained during four meetings so it can be assumed that the trial procedures were effectively standardized. Data were analyzed on an intention-to-treat basis to account for subjects lost to follow-up (3 in total).

A bit surprising for me was that the participants were not prevented from performing other physical exercises during the period of treatment. In controlled trials, this is an approach often used to reduce the influence of confounding variables on the measurement of outcomes. It was not stated which percentage of participants participated in exercise beyond this study’s scope and thus the potential confounding of it on the outcomes cannot be determined. The same was true for the adherence to the home exercise program.

Take home messages

There was no difference in pain outcomes at 6 weeks between the group receiving adductor and the group receiving abductor strengthening exercises. Both approaches can be combined for knee OA. Importantly, the treatment adherence was reported to be high, which may mean the program was feasible. Also, over the 12 weeks, the workload was gradually increased and this was well-tolerated. So, adding hip adductor strengthening to a multimodal approach in knee OA may be possible.

Reference

Peixoto Leão Almeida, G., Oliveira Monteiro, I., Larissa Azevedo Tavares, M., Lourinho Sales Porto, P., Rocha Albano, T., Pasqual Marques, Amé., Hip abductor versus adductor strengthening for clinical outcomes in knee symptomatic osteoarthritis: A randomized controlled trial, Musculoskeletal Science and Practice (2022)