A recent report came across my desk where the provider attempted to assign an impairment rating for a flexion contracture of the knee, and the clinical records clearly showed the pathology objectified was an extension lag. Unfortunately, this is a mistake I see on occasion and can be a huge difference maker in the impairment rating assigned.
Clearly, issues with the overall functionality of the knee can interfere with mobility, comfort, and quality of life. There are two specific clinical situations that are very similar but in reality, are markedly different with respect to the knee.
Defining Flexion Contracture: The Knee That Can’t Fully Straighten
A flexion contracture occurs when the knee cannot fully straighten secondary to a physical limitation, such as tightening or shortening of the soft tissues surrounding the joint. There is a loss of knee extension to both active and passive motion. In short, the knee is “stuck” in a bent (or flexed) position.
Defining Extension Lag: Lacking Active, Not Passive, Extension
The second issue is when the knee does not achieve full extension actively (based on the energy provided by the individual) but passively, that is efforts by other individuals to complete the range of motion, the knee can reach full extension and this is noted as an extension lag.
The Underlying Mechanisms: Why They Differ
Understanding the anatomy of the knee, including the joint capsule, musculature, and other structures is essential. Additionally, an active loss of extension can be a function of scar tissue or other adhesions after knee surgery. Other considerations include arthritis, joint inflammation, such as cerebral palsy. Passive loss of extension can include quadriceps muscle weakness, changes subsequent to a total knee replacement arthroplasty and other factors.
Treatment Approaches: Distinct Paths to Recovery
The distinction matters from several different perspectives. The treatment for a flexion contracture involves stretching, manual therapy, and other physical interventions. At times, surgical intervention may be necessary. Whereas the treatment for an extension lag is addressed by strengthening exercises, neuromuscular reeducation, electrical stimulation and other modalities.
From a workers compensation perspective, an additional concern is the applicable impairment rating. A flexion contracture is an impairable event. However, in extension lag is not. Depending on the severity, this could result in a significant added impairment.
Key Takeaways
In summary, an extension lag is not a flexion contracture. These 2 separate clinical situations may appear to be similar, but differ significantly in their pathophysiology, treatment, and implications for impairment ratings.
The pathology behind each is markedly different, the treatment is different, and the impairment rating assignment is different. A flexion contracture represents a structural limitation, while an extension lag is a muscular control issue.
Understanding this crucial difference is paramount in addressing a workers compensation injury. The differences in rehabilitation, and a misdiagnosis could have far-reaching consequences. For the injured worker, recognizing this distinction would help establish realistic expectations for overall recovery.
This clinical distinction requires careful evaluation and accurate application.