A Biomechanical Comparison between Salter Innominate Osteotomy and Pemberton Pericapsular Osteotomy Salter İnnominate Osteotomisi ve Pemberton Perikapsüler Osteotomisi Arasında Bir

Objective: This study aims to compare the pelvic biomechanics of patients who underwent Salter innominate osteotomy (SIO) for one hip and Pemberton pericapsular osteotomy (PPO) for the other hip. Materials and Methods: Fifty-seven of 126 patients who received a one-stage procedure involving SIO for one hip and PPO for the other hip were included in this series. Preoperative x-rays, archived reports and patient recall were obtained and retrospectively analyzed for these 57 patients. Pelvic biomechanics of the two osteotomy techniques were compared on x-rays and computerized tomography imaging. Results: Based on x-rays, three hips with SIO and 1 hip with PPO had changes that could reflect unstable pelvic biomechanics. SIO caused an average lower limb discrepancy of 0.47 cm in all patients. Positive results were found in 5 patients at their most recent clinical examination. Conclusion: PPO affects the biomechanics of the pelvis much less than SIO. PPO demonstrated ideal biomechanical results compared with SIO, with fewer changes to the pelvic ring and the hip joints.


Introduction
Pelvic biomechanics is an important consideration when deciding on a surgical treatment strategy for developmental dysplasia of the hip (DDH).Salter innominate osteotomy (SIO) and Pemberton pericapsular osteotomy (PPO) affect hip and pelvic biomechanics in different ways, and previous reports in the orthopedic literature have cited the various advantages and disadvantages of each method.Few studies have compared the pelvic biomechanics of these two osteotomy techniques.
In this study, the pelvic biomechanics were compared for a series of patients who underwent SIO for one hip and PPO for the other hip, with correct indications.

Materials and Methods
Fifty-seven out of 126 patients who had undergone a one-stage procedure involving SIO for one hip and PPO for the other hip between 1993 and 2010 were able to be contacted and agreed to be included in this case series.All surgeries were performed with correct indications by one surgeon in our clinic.
Preoperative x-rays, archived reports and patient recall were obtained and retrospectively analyzed for these 57 patients.Intraoperative records were confirmed for each case.At the last clinical examination, postoperative x-rays and computerized tomography examinations were performed on patients to assess hip and pelvic biomechanics.

Results
Lower limb discrepancy poses a potential risk to pelvic biomechanics in patients.We observed equal limb length in 4 patients, a mean 0.66-cm difference in hips treated with PPO (3 patients) and a mean 0.49-cm difference in hips treated with SIO (50 patients).SIO caused an average 0.47-cm lower limb discrepancy.
A positive Trendelenburg test result, which may be assumed to reflect unstable pelvic biomechanics, was found in 5 patients at the last clinical examinations (1 bilateral, 3 hips treated with PPO and 1 hip treated with SIO).
Based on x-rays, 3 hips treated with SIO and 1 hip treated with PPO had changes that may reflect unstable pelvic biomechanics.One hip treated with SIO had had postoperative complications, but for the remaining hips, the intraoperative technique appeared to have caused the instability.

Hip Biomechanics Leading to Dysplasia and Hip Pain
The hip joint is a ball-and-socket joint, and its biomechanics were extensively described by Pauwels in 1976 [1,2].His work showed that to withstand a load, the length of the lever arm of the body weight (which extends from the body's center of gravity to the center of the femoral head) needs to be almost three times that of the abductor muscle lever arm [3].
The development of the femur and acetabulum is related to the directions and power of loads placed upon them.A change in these forces greatly affects the biomechanics between the femoral head and the acetabulum.In the displaced hip, movement of the femoral head from its center of rotation translated into a change to the fixed point of support, as well as changes to the surrounding musculature.In posterosuperior dislocations, the femoral head is displaced posterior and superior of the acetabulum, shortening the abductor muscles [4,5].This movement pulls the greater trochanter upward, and the hip extensors become stronger than the flexors, causing the anteversion angle of the femoral neck to increase.However, this effect subsides by itself after reduction and once balance between the two muscle groups is regained [1,6].Latent anterolateral extraneity refers to the anterolateral-proximal shift of the femoral head; this factor is the most important biomechanical factor in developmental dysplasia of the hip [7].As a result, the posteromedial epiphysis of the femoral head is stressed and becomes asymmetrical.
Hip dysplasia pathology often stems from a shallow, wide acetabulum and a deformed femoral head.Over-anteversion causes the acetabulum to develop in different directions.The femoral collodiaphyseal angle becomes abnormal as the upper portion of the femur is over-anteverted.Halpern et al. identified over-anteversion of femoral heads as the leading cause of hip pain in patients [8].Loading increases the pres-sure on the cartilage by up to 250%.This increase in joint pressure causes compression of the acetabular rims, leading to their thickening and a trigonal shape.When this pressure exceeds the loading resistance levels, bone becomes sclerotic and hyaline cartilage becomes thin or disappears altogether.Pseudocyst formation occurs in the fibrous zone and osteophytes develop in an attempt to withstand the loading.As the hyaline cartilage disappears with the formation of cysts on the femoral head and acetabulum, the joint space closes completely.Osteoarthritis is inevitable when there is uneven loading on chondrocytes [9].The superomedial joint space narrows and, on radiographs, inversion of the labrum appears as superomedial osteoarthritis [10].

Biomechanical Features of Salter Innominate Osteotomy
Although the technical aspects and results of SIO have been previously reported, there are insufficient data examining the mechanical changes to the hip and peripheral tissues [11].SIO is applied from the greater sciatic notch to the anterior inferior iliac spine (AIIS).The distal fragment is able to be overturned inferolaterally by the flexibility of the symphysis pubis [12][13][14][15].The distal fragment is rotated along the axis between the symphysis pubis and the greater sciatic notch.The acetabulum is re-orientated as it is extended and adducted.This rotation allows the muscle groups to lengthen.The osteotomy is held open by a triangular-shaped bone graft that is wedged between the AIIS and the center of the hip joint.The maximum displacement required by the distal fragment is achieved by a specific size of bone graft [11,15].For example, a 3-cm-thick graft is utilized for a 30° graft angle [11,12].This wedge extends and retroverts the acetabulum around a fixed axis.
A lack of contact with the posterior osteotomy line causes a mechanical load to the graft.The graft becomes unstable, and the acetabulum continues to move distally [11,12].Corrections of 22° (8°-34°) on the anteversion angle and 9.5° (2°-18°) on the inclination angle can be obtained.According to Salter, instability may also arise secondary to formation of a hernia pouch of the capsule.In these situations, capsulorrhaphy is also necessary.Tachdjian states that plication with excision of the extracapsular region and capsular repair using stretched sutures is the best way to obtain stability [16][17][18].
As a result, SIO gradually re-orientates the hip joint center to migrate distally, posteriorly and medially, and the acetabulum extends between the osteotomy lines, limiting the adduction of the acetabulum.After osteotomy, there is increased tightness of the hip flexors and abductors [12].SIO increases the percentage of femoral head covered by the acetabulum, preventing advanced subluxation of the femoral head and subsequent arthrosis [4] and also permitting the cartilage to develop normally [19].

Biomechanical Features of Pemberton Pericapsular Osteotomy
PPO is an incomplete osteotomy.Its creator, Pemberton, emphasizes acetabular shallowness and insufficiency in the antero-superior acetabular regions as the primary problems.He also states that the triradiate (Y) cartilage can be used as hinge to modify the acetabular shape and volume and that sufficient anterolateral femoral head coverage can be obtained by using the iliopubic and ilioischial ramus as a hinge [20].Pemberton proposed that this technique was suitable for children with dislocated or subluxated hips prior to early adolescence when the flexibility of Y cartilage is lost, i.e., from 1 until 12 years of age for girls and up to 14 years for boys.The success of the operation is closely related to the flexibility of the Y cartilage and the subsequent acetabular remodeling.This hinge effect provides more correction to the acetabular index by reducing the angle and generating less rotation, making the pelvis physiologically more stable.As there is change to the inside volume of the pelvis, there is no risk of narrowing the birth canal.However, PPO can change the acetabular configuration and capacity and can cause a loss of adaptation between the femoral head and the acetabulum in later life.
The biggest concern with SIO is the difficulty in obtaining a stable position for fragments demonstrating sacrospinous rigidity.As PPO causes no changes to the posterior wall, sacrospinous changes are also minimal [21].For this reason, PPO is a good choice for patients with sacrospinous rigidity.
Because PPO is an incomplete osteotomy, the pelvic ring is unchanged and the pelvic volume and therefore the birth canal do not change [21,22].Neither the use of K-wires nor their subsequent extraction is required [20], and the risk to the sciatic nerve and superior vasculature is low [21].Pemberton reports 94.3% success with this technique [23].
In conclusion, SIO replaces the hip joint center distally, posteriorly and medially.Adduction of the acetabulum becomes restricted, and the abductor and flexor group muscles become more flexible.PPO, in contrast, is an incomplete osteotomy and does not alter the pelvic ring or size of the birth canal.The graft is placed tightly in line with the osteotomy, and stabilization with K-wires is not required.According to the findings in this study, PPO affects the biomechanics of the pelvis much less than does SIO.Overall, PPO demonstrated better biomechanical results than SIO with fewer changes to the pelvic ring and hip joints.