A recent study published by the journal European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) determined that vitamin D levels below 12 ng/ml were associated with impaired early functional outcomes among patients who underwent total knee arthroplasty.
Knee osteoarthritis (OA) occurs when the cartilage surface of a joint begins to degenerate over time. As the damage to the joint progresses, individuals encounter a significant amount of pain and functional impairment. When the OA becomes severe, surgery is the best option to relieve the pain and increase functionality.
Total knee arthroplasty (TKA) is a common surgical procedure for those with end-stage knee osteoarthritis in which the damaged cartilage and bone of the knee joint is replaced with artificial parts. The overall prognosis for TKA patients is high, as it results in significant pain relief and an improved quality of life. However, due to the invasiveness of the procedure, patients often face bone and muscle damage, as well as a prolonged recovery time.
Since vitamin D is important in maintaining bone and muscle health, researchers believe that vitamin D status may play a crucial role in the development and management of knee osteoarthritis. One study suggests that low vitamin D status significantly increases the risk for the progression of knee osteoarthritis. Another study found that vitamin D may improve osteoarthritis pain through its role in muscle strength. However, whether vitamin D plays a role in TKA outcomes remains unclear.
Therefore, in a new study, researchers aimed to determine whether vitamin D status affects early functional outcomes after TKA. A total of 87 patients diagnosed with primary TKA were included in the study. The researchers gathered the participant’s anthropometric data and obtained preoperative vitamin D status. There were no significant differences in the study population, aside from 25(OH)D levels. The patients were then divided into two groups: those who were vitamin D deficient (< 12ng/ml) and those who were vitamin D non-deficient (> 12ng/ml). The researchers used the following tools to determine the patient’s functional independence one day before and three months after the TKA:
- The American Knee Society Score (KSS) is a standard system used to evaluate the joint and the individual’s functional ability to walk and climb stairs. The patients are scored out of 100, with a higher score indicating a greater level of functional independence.
- The Alternate Step Test (AST) involves the shifting of weight, allowing the researchers to measure lateral instability.
- The six-meter walk test (SMT) evaluates the time it takes for the patients to walk six meters.
- The sit-to-stand test (STS) assesses how quickly the patients are able to rise from a chair without the use of their arms.
- The timed up and go test (TUGT) measures the time it takes individuals to get out of their chair, walk 3-meters and return to their original position.
Did the researchers observe a relationship between vitamin D status and TKA functional outcomes? Here is what they found:
- The mean vitamin D status of the vitamin D-deficient group was 9.1 ng/ml (6.8-10.8 ng/ml); whereas, the mean vitamin D status of the vitamin D non-deficient group was 18.3 ng/ml (15.6-26.0 ng/ml; p < 0.001).
- The vitamin D-deficient group experienced significantly lower post-operative function KSS outcomes than the vitamin D non-deficient group (67.2 vs. 73.4, respectively; p = 0.031).
- The mean post-operative AST times were significantly longer in the vitamin D-deficient group compared to the vitamin D non-deficient group (8.8 vs. 7.7, respectively; p = 0.012).
- The mean post-operative SMT times were significantly longer in the vitamin D-deficient group compared to the vitamin D non-deficient group (16.6 vs. 14.6, respectively; p = 0.003).
- Although not statistically significant, both the post-operative STS and TUGT scores showed an increased time in the vitamin D-deficient group compared to the vitamin D non-deficient group (12.7 vs. 11.7 seconds, respectively; p > 0.05).
The researchers summarized their findings:
“The most important finding of the present study was that early post-operative outcomes following TKA were affected by patients’ preoperative vitamin D status, and those in the vitamin D-deficient group had significantly poorer post-operative outcomes.”
They went on to state,
“These findings indicate that surgeons should confirm vitamin D status before performing TKA and consider preoperative vitamin D supplementation for patients with vitamin D deficiency.”
It is important to note that none of the participants included in the study were vitamin D sufficient, based off the Vitamin D Council’s and the Endocrine Society’s standards. Levels below 30 ng/ml may result in the overproduction of parathyroid hormone and inadequate absorption of calcium, which can negatively affect bone health. Furthermore, research suggests that maintaining a vitamin D status of 40 ng/ml to 60 ng/ml likely offers additional benefits beyond bone health. With the understanding of the long term effects of vitamin D deficiency on bone and muscle health, the Vitamin D Council recommends individuals supplement with 5,000 IU vitamin D3 daily when they are unable to receive safe, sensible sun exposure.
This study provides a foundation for future research. Since the study is limited by its relatively short follow-up and observational design, large scaled clinical trials are warranted to determine if a causal relationship exists between vitamin D and recovery from TKA.
Sturges, M. & Cannell, JJ. Vitamin D deficiency associated with impaired functional outcome after total knee replacement surgery. The Vitamin D Council Blog & Newsletter, 2016.
Shin, Keun-Young, et al. Vitamin D deficiency adversely affects early post-operative functional outcomes after total knee arthroplasty. European Society of Sports Traumatorlogy, Knee Surgery, Arthroscopy (ESSKA), 2016.