Participants and ethics statement
The animal protocols for this study were approved by the Laboratory Animal Welfare and Ethics Committee of Third Military Medical University (project number: AMUWEC20211776). Skeletally mature Chinese miniature pigs, weighing 20-25 kg were included in the study of porcine model construction for specific hip conditions. All methods were carried out in accordance with the National Research Council’s Guide for the Care and Use of Laboratory Animals and the study was reported according to the ARRIVE guidelines.
Two 6-month-old pigs were sacrificed to explore the anatomy of the hip including musculature, neurovascular structures, and soft tissues like capsule. We have found that there exists generally three layers of muscle group surrounding hip joints. The superficial layer lies the tensor fasciae latae, gluteus suferficidlis, quadriceps femoris, and biceps femoris (Figure 1A). Underneath the tensor fasciae latae and gluteus suferficidlis lies the gluteus medius (Figure 1B). The distal end of the gluteus medius is the greater trochanter and the dorsal end is the ilium. The gluteus profundus is exposed when flipping over the gluteus medius (Figure 1C).
As mentioned above, the hip joint lies right under the gluteus medius, which is either faced or bypassed when the superficial layer of muscle groups is incised for exposure. We have found that both going anterior and posterior to the gluteus medius can reach the central compartment (Figure 2B, D). We have also considered bluntly dissecting the muscular part and going right through the middle of the gluteus medius, which provides the best operative exposure and the least surgical tension (Figure 2C). Based on the cadaveric finding, we have come up with three possible approaches to build a porcine model: anterior approach, transgluteal approach, and posterior approach.
The potential risk of each approach
The most vital neurovascular structure including sciatic nerve, arteria femoralis caudalis, and posterior femoral vein courses along the dorsal side of the gluteus profundus and is covered by gluteus medius (Figure 3A, B). The distance between the neurovascular structure and the posterior side of the hip joint is approximately 1 cm (Figure 3C). Therefore, using the posterior approach might increase the chance of main neurovascular structures injury, especially the sciatic nerve. As for the anterior approach, it was noted that various vascular branches were against and cut off for exposure when each layer of muscles were incised to reach the central compartment (Figure 3 D, E, F). Thus extra blood loss would possibly be the underlying risk of the anterior approach. Despite the lower risk of neurovascular injury in transgluteal group based on the cadaveric findings, there might be a potential risk of muscular dysfunction in transgluteal approach.
36 Chinese miniature pigs (6 months old of age and weighing 20-25 kg) were evenly divided into three groups in a random way according to the undergone approaches: anterior, posterior, and transgluteal group. All groups of pigs were used as models of irreparable acetabular labral tear and received subsequent treatment of labral reconstruction.
The porcine is placed in a lateral position on an operating table and surgical incision is marked (Figure 4A).
An autogenous Achilles tendon graft is used for this technique. A longitudinal incision is made posterolateral to the ankle in line with the long axis of the tibia. The lateral haft is harvested along the Achilles. The length of harvested graft is supposed to be about 15 mm. Any remaining muscular or fatty tissue is cleared after graft harvest. Because of the initial tubular shape of the Achilles tendon graft, the step of graft tubularization using sutures is skipped. (Figure 4B)
The pigs were anesthetized by inhaling isoflurane with a concentration of 2.5-3%. After skin disinfection and draping (Figure 4C), a straight incision was made directly above the greater trochanter. The skin, subcutaneous superficial fascia, and aponeurotic fascia were incised. Tensor fasciae latae was incised between tensor fasciae latae and quadriceps femoris to expose the gluteus medius (Figure 5A). The transgluteal group underwent blunt dissection of the musculus gluteus medius to reach the capsule. Meanwhile, gluteus medius was pulled anteriorly or posteriorly with a retractor for exposure in the anterior and posterior groups (Figure 5 B, C, D). Following that, the gluteus profundus was exfoliated to incise the capsule and the labrum was exposed (Figure 5 E). A 1.0 cm-long anterior labrum was resected and the labral defect was reconstructed with the prepared graft secured to the acetabular rim using nonabsorbable 3-0 sutures (Ethicon) (Figure 5F).
Postoperatively, the pigs were injected with penicillin intramuscularly twice to prevent infection. There is no weight-bearing restriction or immobilization during the recovery period.
Evaluation of safety and efficiency
All pigs were followed up until three months postoperatively, at which time points the surviving pigs were sacrificed. Intraoperative blood loss and operative time of all pigs were recorded. Surgical exposure was rated from 0-10 points, where10 stands for an excellent operative field, and 0 means exposure is absolutely not enough for operation. At the endpoints of follow-up, any postoperative complications were recorded and survival curves were analyzed.
All statistical analyses were performed with SPSS (version 21, SPSS Inc, Chicago, IL) and GraphPad Prism 7.0 software (GraphPad, La Jolla, CA, USA), and a P value<0.05 was considered statistically significant. Continuous values were compared between two groups with 2-tailed Student t-tests. Survival curves were analyzed using the Kaplan-Meier method and compared with the long-rank test.