Investigation of sensory nerve endings in pulvinar, ligamentum teres, and hip joint capsule: A prospective immunohistochemical study of 36 cases with developmental hip dysplasia.

OBJECTIVE

The aim of this study was to immunohistochemically identify and characterize the presence of sensory nerve endings (SNEs) in pulvinar, ligamentum teres (LT), and hip joint capsule (HJC) of children with developmental dysplasia of the hip (DDH).

METHODS

Pulvinar, LT, and HJC specimens were obtained from 38 hips of 36 children (31 girls, five boys; mean age=49 months; age range=18-132 months) during open reduction surgery for DDH. All specimens underwent subsequent routine tissue processing (formalin fixation and paraffin embedding). To determine tissue morphology, haematoxylin and eosin staining was used. SNEs were analyzed immunohistochemically using a mouse monoclonal antibody against S-100 Beta Protein based on the classification of Freeman and Wyke including four types of SNEs including mechanoreceptors: type I Ruffini corpuscles, type II Pacini corpuscles, type III Golgi organs, and type IVa unmyelinated free nerve endings (FNEs). Additionally, children were sorted into three groups based on their age at the time of surgery: Group 1 (age <3 years; 19 hips of 18), Group 2 (age: 3-5 years; 10 hips of 10 children), and Group 3 (age >5 years; 9 hips of 8 children).

RESULTS

Although no Type I, II, or III SNEs were identified in any specimen, type IVa mechanoreceptor (FNEs) was immunohistochemically characterized in 13 (34%) pulvinar, 19 (50%) LT, and 16 (42%) HJC specimens. The total density of FNEs was 3.31±5.70)/50 mm2 (range 0-21) in pulvinar specimens, 3.18 ± 5.92)/50 mm2 (range 0-24) in HJC specimens, and 4.51±6.61/50 mm2 (range 0-22) in LT specimens. Furthermore, the operated side, gender, and the number of FNEs in specimens did not differ significantly among the age groups (p>0.05 for all), and the number of FNEs was not significantly correlated with age, gender, or the operated side (p>0.05 for all).

CONCLUSION

Evidence from this study revealed that pulvinar, LT, and HJC include only FNEs, which play a role in pain sensation, among mechanoreceptors. Surgical excision of these tissues may not cause a significant loss of sensory function in the hip joint of children with DDH.

LEVEL OF EVIDENCE: Level II, Therapeutic Study.