Hip Replacement in Children with Femoral Head Collapse and Hip Joint Degeneration—Two Case Reports

There are several pathological conditions in children, such as Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, and femoral head avascular necrosis, which can progress to disabling hip joint destruction. These children undergo surgeries, such as hip arthrodesis, in an attempt to postpone hip replacement so that it can be done at an older age. Unfortunately, hip arthrodesis significantly limits their ability to actively engage in activities that require full hip mobility. For these children, active participation in games and sports activities remains an important factor for their physical development and mental health. On the contrary, hip arthroplasty can ensure a pain-free, unrestricted range of hip movement, but are doubts as to its viability over time, especially in young people who exhibit intense activity. We report successful hip replacement in two children, fourteen years of age and younger, with femoral head collapse and disabling joint degeneration due to avascular necrosis of the femoral head, whom the hip replacement was considered the only surgical treatment ensuring a painless hip joint. For the clinical assessment of these two hips, we used the online Harris hip score, preoperatively and postoperatively. No intraoperative or early postoperative complications occurred. Follow-up was conducted at six weeks, six months, and then at an annual clinical and radiological evaluation. At the final seven-year follow-up, these two children had greatly improved their function hip score considerably. Hip arthroplasty can ensure a pain-free, unrestricted range of hip movement in young children when their hip joint is severely affected.


Introduction
Avascular necrosis (AVN) of the femoral head is a pathologic process that results from the interruption of the blood supply to the bone [1]. Femoral head ischemia, traumatic or nontraumatic, causes the death of the bone marrow and usually results in the collapse of the necrotic segment [2,3]. Traumatic causes of femoral head AVN in children include femoral neck fractures, traumatic hip dislocation, and slipped femoral capital epiphysis [4,5]. The non-traumatic form of AVN of the femoral head in children is mainly associated with septic arthritis, thrombocytosis, chemotherapy, radiation, Gaucher disease, sickle cell disease, high doses of corticosteroids, and finally with idiopathic avascular necrosis [6,7]. In the early stages of AVN (pre-collapse stage of the femoral head), core decompression is typically considered the most appropriate treatment [8][9][10][11][12][13]. It decreases the intraosseous pressure in the femoral head and increases blood flow to the necrotic area, thus augmenting new bone formation.
In the late stages of AVN (collapse stage of the femoral head), the AVN can progress to joint deterioration and lead to osteoarthritis of the hip joint. Hip arthroplasty (HA) is the recommended surgical treatment for these young patients [14][15][16]. In children, despite the advances in hip conserving techniques, such as mesenchymal stem cells implantation [17][18][19][20], vascularized or nonvascularized bone grafting [21][22][23], muscle pedicle bone grafting [24][25][26], trans-trochanteric rotational osteotomy, and intertrochanteric varus or valgus osteotomy [27][28][29][30][31], the hip disease can progress to disabling joint destruction. HA is rarely recommended in skeletally immature patients. There are concerns about implanting prostheses in children. These include poor bone stock, leg length discrepancies, and small femoral canals. Surgeons are also cautious about the need to revise prostheses, as the implants to most pediatric patients are unlikely to survive. Therefore, young patients with disabling hip disease will often undergo other surgical procedures, such as hip arthrodesis in an attempt to extend the survivorship of the pediatric hip and thus postpone HA [32,33]. Despite all these concerns, HA can ensure a pain-free, unrestricted range of hip movement. For these children, active participation in games and sports activities remains an important factor for their physical development and mental health. Sedrakyan et al. reported a rate of revision surgery in the pediatric and young adults population, after HA, similar to that of the older patients [34]. The cumulative percent revision at five years was 4.6%. The importance and objective of our study were to emphasize the necessity of using HA in children with disabling hip joint destruction as with it is ensured a pain-free, unrestricted range of hip movement.

Patient Information
A 14-year-old boy was referred to our institution for treatment of his painful and rigid left hip joint, a condition that made him unable to walk without the help of crutches.

Past History
His symptoms started one year ago with an insidious onset of pain in his left groin region. The X-ray of the hip was normal at that time (Fig. 2a). The laboratory blood tests were negative for the presence of infection of the hip. The physician recommended bed rest for a few days and restriction from sports activities for a few months. Four months later, the gradual increase of the pain and stiffness in the left hip necessitated the patient's hospitalization for ten days to ensure hip immobilization. The laboratory blood tests were again negative for the presence of infection of the hip. The X-ray at that time revealed a flattening of the lateral half of the capital femoral epiphysis (Fig. 2b). Ten months later, due to deteriorating hip symptoms, he was referred to our institution for further treatment. The X-ray revealed the collapse of the femoral epiphysis (Fig. 2c).

Clinical Findings
On clinical examination, a fixed 30° flexion deformity of the left hip was obvious, accompanied by a severe restriction of its movements.

Therapeutic Interventions
Hip replacement was considered the only surgical treatment capable of ensuring a painless hip joint. The patient received a femoral head resurfacing implant (no traditional THR) utilizing an uncommon implant (Birmingham Mid Head Resection Prosthesis). It is a metal-on-metal articulation. Although the use of a metal-to-metal prosthesis for adolescents is controversial now, the Birmingham Mid head resection implant (BMHR) was chosen, wrong in my current opinion, as the most suitable for this patient at that time ( Fig. 2d). This decision was based on the belief that this ensures the preservation of the femoral neck and 1/3 of the femoral head, postponing the total hip replacement for much later, thus gaining time, which is very important for this patient, mainly due to his young age.

Surgical Technique
To avoid failure of the femoral component of the arthroplasty, and the possible femoral neck fracture, the placement of the femoral component of the prosthesis in the valgus position was considered obligatory. Placing the femoral component in the valgus position increases the required compression forces and reduces the harmful shear forces, acting on the preserved femoral neck. In addition, the placement of the femoral component in the valgus position obliges the most horizontal placement of the acetabulum component (reduced angle of inclination of the acetabulum, 22°), thereby ensuring the congruity of the hip joint implant (Fig. 2d).

Follow-up
For the clinical evaluation of the patient preoperative and postoperative, we used the online Harris Hip Score (Orthotoolkit) ( Table 1). No intraoperative or early postoperative complications occurred. The clinical and radiographic follow-up was conducted at six weeks, six months, and then annually (Fig. 3). Full weight-bearing without aids allowed 4 weeks postoperatively. The X-ray of the hip was normal at that time. The physician recommended bed rest for a few days and restriction from sports activities for few months. b Four months later, the gradual increase of the pain and stiffness in the left hip necessitated the patient's hospitalization for ten days to ensure hip immobilization. The X-ray at that time revealed a flattening of the lateral half of the capital femoral epiphysis. c Ten months later. The X-ray revealed the collapse of the femoral epiphysis due to necrosis of the femoral head.   (Fig. 4)

Patient Information
A 13-year-old overweight boy was referred to our hospital for treatment of his painful and rigid right hip joint, a condition that made him unable to walk without the help of crutches.

Past History
It was started with an unstable, acute slipped capital femoral epiphysis (25° posterior tilt) that was partially reduced and treated surgically with fixation of the slipped capital femoral epiphysis with a single screw. The clinical and radiographic follow-up conducted at six weeks, and then at regular intervals of two months, revealed a progressive deterioration of the pain and stiffness of the right hip and progressive destruction of the capital femoral epiphysis due to avascular necrosis. The follow-up, thirteen months postoperatively, revealed femoral head collapse and disabling degeneration of the hip joint (Fig. 5a). The single hip screw was removed five months later (Fig. 5b, c). Hip replacement was considered the only surgical treatment capable of ensuring a painless hip joint and was performed five months after the removal of the hip screw.

Clinical Findings
On clinical examination, a fixed 40° flexion deformity of the right hip was obvious, accompanied by a severe restriction of its movements.

Therapeutic Interventions
Total hip replacement was considered again the only surgical treatment capable of ensuring a painless hip joint. Autologous bone grafting of the reconstructed acetabulum, using as graft the excised femoral neck, was considered necessary, due to the thinning of the acetabular  (Figs. 6, 7).

Follow-up
For the clinical evaluation of the patient preoperative and postoperative, we used the online Harris Hip Score (Table 1). No intraoperative or early postoperative complications occurred. The clinical and radiographic follow-up was conducted at six weeks, six months, and then annually. Full weight-bearing without aids allowed 4 weeks postoperatively. On the immediately post-operative AP radiograph, the acetabular component of the implant appears to penetrate the medial wall of the acetabulum, but seven years postoperatively, the position of the acetabular component of the implant appears to be unchanged (Fig. 8).

Results
In the first case, during the seven-year follow-up, the hip function score improved significantly from 29.55 points preoperatively to 93 points postoperatively ( Table 2). In the second case, during the seven-year follow-up, despite the radiographic appearance of the penetration of the acetabular   (Table 3).

Discussion
Total hip replacement is the most commonly used hip arthroplasty worldwide.
In the hip resurfacing arthroplasty, 2/3 of the femoral head are removed, while the neck and 1/3 of the femoral head are preserved. To the preserved femoral head, a ceramic or metal ball is attached. An artificial cup with metal or ceramic lining replaces the socket in the acetabulum.
In the past, in young patients with rheumatoid arthritis, bone cement was commonly used to hold hip implants in place [35]. Nowadays, in young patients, uncemented implants are regularly used, with the results of the uncemented THA being more positive than those of cemented THA [36][37][38][39]. Uncemented implants have a coarse surface that allows the bone to grow into it and adherent to it. In the hybrid total hip replacement, the cup is positioned firmly into the socket cementless while the femoral component is placed into the femoral canal with cement for its stabilization.
Current trends in prosthesis design emphasize the use of materials that are strong enough to withstand the more active lifestyles of many patients, while generating minimal wear debris. The materials that are used to make hip implants are made of polyethylene (plastic), metal, ceramic, or a combination of them.
Metal-on-metal (MoM) implants are no longer available in the USA since worries have been upraised about the potential long-term systemic effects of metal ion toxicity in the blood due to the fact that metal materials can shed metal particles into the bloodstream, causing serious health problems such as cancer and heart failure [42]. However, large cohort studies have currently observed that patients with metal-on-metal hip bearings are not at increased risk of cancer, heart failure, or mortality compared to other hip replacement patients [43].
Ceramic-on-polyethylene (CoP) implants combine a ceramic ball with a plastic cup. The plastic cup can create plastic debris, which can cause the implant to fail [40,41].
Ceramic-on-metal (CoM) implants combine a ceramic ball with a metal lining cup.
Ceramic-on-ceramic (CoC) hip implants combine a ceramic head with a ceramic lining cup. The results of using ceramic-on-ceramic bearing surfaces in young patients are very encouraging [44][45][46]. Ceramic-onceramic implants have been demonstrated to provide the lowest wear rates in comparison to other material options used for THA [47][48][49]. The most common failures of these devices are associated with loosening of the lining and fracture of the components.
Children with disabling joint destruction are unable to participate in sports activities that require full hip mobility. These children undertake surgeries, such as hip arthrodesis, in an attempt to postpone hip replacement so that it can be done at an older age [32,33]. Unfortunately, hip arthrodesis significantly limits their ability to actively participate in activities that require full hip movement. For these children, active participation in games and sports activities remains an important factor for their physical development and mental health. On the contrary, hip arthroplasty can ensure pain-free, unrestricted hip mobility, but there are worries as to its viability over time, especially in young people who demonstrate intense physical activity [50][51][52]. Additionally, there are worries concerning inadequate bone stock, leg length discrepancies, small acetabulum, and small femoral canals.
Finally, despite the fact that our study involves only two cases, and thus no safe conclusions can be drawn, our results are no different from those already published so far [34]. However, more recent studies have focused on adolescents and young adults, with only a few studies involving patients younger than 16 years of age [53,54]. The data from these children were gathered for analysis, with a greater proportion of THA performed in older patients. Information on the outcome of the up-to-date THA in very young patients with disabling hip joint destruction is therefore missing.

Conclusion
Due to the demands for increased durability and survival of hip arthroplasty, a cementless prosthesis and more specifically ceramic-on-ceramic implants are currently recommended for THR in children, and we agree with this view. As for our preference between the two used types of hip arthroplasty, we prefer the traditional THA.