Abstract
BackgroundThe mechanism of pain after meniscus injury remains unknown. After injury, some individuals suffered from acute pain, while others suffer from delayed pain. A precise nociceptor distribution pattern may provide the answer to this question.MethodsTwenty-two intact menisci (paired medial and lateral menisci) were obtained from 11 patients with a mean age of 28.45 years. All menisci were sectioned into five parts: the anterior horn, anterior body, middle body, posterior body, and posterior horn. Two paired menisci were stained by a modified gold chloride method. All other specimens were stained by H&E staining and were subjected to immunohistochemical staining to detect substance-P (SP). Under a microscope, measurements were made in 10 consecutive visual areas at 400x magnification. SP-positive fibres were determined using a three-grade scale, and the mean number of SP-positive fibres was assessed.ResultsNerve fibres and nociceptors stained by H&E and modified gold chloride were found mainly in the vascular outer third of the menisci as observed under a microscope; the positive area was wider in the anterior and posterior horns. There were more SP+ fibres in the anterior horn and posterior horn than in the anterior body, middle body, or posterior body (p < 0.05). Regarding the bodies, the mean number of substance-P fibres was greater in the anterior body or posterior body than in the middle area (p < 0.05). No significant differences were found between the number of substance-P nerve fibres in the anterior horn vs the posterior horn or in the anterior body vs the posterior body of all menisci (p > 0.05). No significant differences were observed in the same location between the paired medial and lateral menisci in all areas of the menisci (p > 0.05).ConclusionThe density of nociceptors decreased along the longitudinal axis of the meniscus from both horns to the middle part of the body, which may guide future diagnostic methods and rehabilitation protocols.
Highlights
The meniscus plays an important role in biomechanics, such as load bearing, load transmission and joint congruity
Chondrocytes were gathered into a round, oval or fusiform area and Histological evaluation Nerve fibres that were positive for substance-P (SP+), which is specific to nociceptive fibres, were detected in all five portions of the menisci, but the distribution density varied in each part (Fig. 4)
Compared with gold chloride staining, immunohistochemical staining showed that SP+ fibres were fewer in number, and the SP+ zone was narrower than the gold chloride-stained positive area
Summary
The meniscus plays an important role in biomechanics, such as load bearing, load transmission and joint congruity. When the meniscus is torn, pain is usually the most common symptom [1]; the mechanism of pain remains unknown. Some patients suffer acute pain immediately, while others do not. Meniscus injury in those patients without obvious symptoms cannot be detected until the injury progresses and a locked knee develops. A physical examination or magnetic resonance imaging is used to diagnose meniscus injury [2]. Degenerated diseases such as extrusion of the meniscal body can be asymptomatic and lead to osteoarthritis [3]. Understanding the distribution of nociceptors responding to noxious stimulus may provide answers to this question. A precise nociceptor distribution pattern may provide the answer to this question
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