From the Guidelines
The answer is (b) weak dorsiflexion, as an L5-S1 disc lesion typically affects the S1 nerve root, which can also impact the L5 nerve root, leading to weak dorsiflexion. When considering the impact of an L5-S1 disc lesion on nerve roots, it's crucial to understand that this lesion can compress or irritate the S1 nerve root, which is primarily responsible for foot plantarflexion and ankle reflexes, but can also affect the L5 nerve root, leading to symptoms such as weak dorsiflexion 1. The L5 nerve root controls muscles involved in dorsiflexion of the foot, among other functions. Given the proximity of the L5 and S1 nerve roots at the L5-S1 disc level, a lesion here can lead to a complex presentation of symptoms, including both sensory and motor deficits 1. However, the most direct and significant impact related to the options provided, considering the typical presentation and the anatomy involved, points towards weak dorsiflexion as a potential consequence of an L5-S1 disc lesion. It's essential to conduct a thorough neurological examination, including assessment of knee strength and reflexes, great toe and foot dorsiflexion strength, and foot plantarflexion and ankle reflexes, to accurately diagnose and manage the condition 1. This approach ensures that the morbidity, mortality, and quality of life outcomes are prioritized by providing an accurate diagnosis and appropriate treatment plan tailored to the patient's specific condition.
From the Research
L5-S1 Disc Lesion Symptoms
- The symptoms of an L5-S1 disc lesion can vary, but according to the studies, it is likely to result in:
- Weak plantar flexion, as S1 radiculopathy is usually presented with foot plantar flexion/eversion weakness 2
- Lost sensation in the lateral aspect of the foot, as S1 radiculopathy can cause hypoesthesia in this area 2
- Weakness of ankle inversion, plantar flexion, and foot drop, as these are main clinical manifestations of the sacral plexus lesion area 3
- The options provided can be evaluated as follows:
- (a) weak plantar flexion: This is a possible result of an L5-S1 disc lesion, as it can cause S1 radiculopathy, which is usually presented with foot plantar flexion/eversion weakness 2
- (b) weak dorsiflexion: This is not directly mentioned as a result of an L5-S1 disc lesion, but foot eversion is usually stronger than foot dorsiflexion in patients with sacral plexus lesion 3
- (c) absent knee jerk: This is not mentioned as a result of an L5-S1 disc lesion in the provided studies
- (d) lost sensation in the big toe: This is not directly mentioned as a result of an L5-S1 disc lesion, but numbness and decreased sensation can be present along the anterolateral calf and dorsum of the foot 3