| BackgroundTotal hip arthroplasty (THA) has been used, successfully and effectively, for the treatment of various advanced stage hip diseases, such as osteoarthritis, rheumatoid arthritis, congenital acetabular dysplasia, avascular necrosis of the femoral head for decades. Harris firstly reported a modular prosthesis in1971, which promoted the development of various materials and the interface combination, and provided surgeons more choices, but also brought wearing, separation, loosen of prosthesis and other complications. Over the past20years, most of THA were composed of metal or ceramic head and traditional polyethylenes (PE) liner. The worn liner, periprothetic osteolysis and prosthesis aseptic loosening resulted from PE particles, were the main reasons of revision.There are mainly two kinds of techniques in acetabular prosthesis revision, total acetabular revision and isolated acetabular liner exchange. Total acetabular revision with bone grafting if necessary, become a consensus in management of acetabular loosening. For the stable metal acetabular cup with worn liner and various degree of periprothetic osteolysis, the choice of total acetabular revision or liner exchange remains controversial. Lots of surgeons prefer to liner exchange, for which have the advantage of mimic invasive, less bleeding, time and cost effective, bone reservation, eliminating wearing particles and membrane at the same time. Osteolysis can be treated by allograft bone grafting through acetabular screw holes or by fenestration. Liner exchange can avoid acetabular bone defect and pelvic discontinuity, reduce operation disability and mortality rate.Liner exchange can be divided into simple liner exchange and cemented liner technique. The later which is so-called double-socket technique means a liner was fixed into the original metal acetabular cup with cement. Simple liner exchange is often difficult to carry out because of a damaged locking mechanism (by wear, fatigue or trauma), lack of a replacement liner in desire material or size, and so on. While cement liner technique that fixed a new liner into the original metal acetabular cup with cement, can not only avoid the problems above, but also prevent revision from infection by using antibiotics cement. Cement liner technique can change prosthesis interface to metal liner or other material. Liner with different sizes can be chosen to cement in the original acetabular cup, concerning about the diameter of the femur head and the thickness of liner.Cemented liner technique in clinical was firstly reported by Heck and Murray in1986and then spreaded worldwide in extensive research and clinical application. Biomechanical studies suggested that the interface fixation of liner-cement-metal acetabular cup was stronger than or comparable to the acetabular standard locking mechanism. Meanwhile, cemented liner technique had also achieved excellent results in clinical or radiographic follow up. The replacement liner, especially the highly cross-linked polyethylene liner could prevent patient from progress or recurrence of osteolysis because of low wear rate and reduce wear particles generated from polyethylene-on-ceramic or polyethylene-on-metal interface. Combined with allograft bone grafting through screw holes or by fenestration in osteolysis area to remove the interface membranes, wear particles and granulation tissue, eliminate osteolysis and recover the bone mass of host acetabulum, cemented liner technique can also promote bone ingrowing with the porous surface of acetabular cup. Although cemented liner technique achieved excellent results, its complications could not be ignored. The rates of hip dislocation after revision were high (range,15%-30%) for several reasons. This technique was limited to the direction of previous acetabular cup. Cemented liner in the acetabular cup of retroversion or excessive abduction made the hip in high risk of dislocation and interface separation. Some authors believed that there were some correlation between dislocation after revision and operative approach. The posterior approach debridement of scar and resection of joint capsule might lead to dislocation, while there was an extremely low rate of hip dislocation in liner revision using lateral or anterior approach.The proper choice of indication is critical for operation. Cemented liner technique is mainly for the management of the stable acetabular cup with liner wear, damage of locking machanism, lack of liner to match the original acetabular cup. Sometimes, the indications were relative. The healing strategy were adjusted accordingly, such as the local osteolysis need liner revision combined with allograft bone grafting in the osteolysis zone, while extensive or periprosthetic osteolysis should be considered the total acetabular revision. If the acetabular cup had been used for a long time which approach to the prosthesis longevity, the total acetabular revision may be a proper choice, otherwise, cementing a liner will be a good selection. If a patient has a history of dislocation or a mal-positional acetabular cup in his artificial hip joint, liner replacement should be careful for the high risk of dislocation. Most of surgeons prefered to choose total acetabular revision in this condition.Malposition of artificial acetabulums, such as neutral or backward place, excessive abduction of the metal acetabular cups, is a common defection. Excessive abduction result from seeking osseous containment for getting a satisfactory fixation of acetabular cup, increase liner wear at upper parts. For such cases, whether it is feasible and reliable that a new liner cemented and rolling in an unsatisfied acetabular cup till to a correct abduction or anteversion angle is not reported in our knowledge but a practical topic.Therefore, we focus our attention on this topic to provide whether cemented liner technique is suitable for such cases for avoiding total acetabular revision preserving bone mass and preventing patient from dislocation.Objective1. To compare hip Harris score between surgeon’s result and patients’ self-evaluation. To access the correlation between abduction angle of acetabular cup and the liner wear, investigate the incidence rate of excessive abduction acetabular cup (≥50°,≥55°), and illustrate the necessity of cemented liner technique in the stable but dys-directional acetabular cup.2. To evaluate the strength of liner-cement-metal cup interface in cemented liner technique, and assess whether the interface fixation of liner-cement-metal cup is more strength than or equivalent to the acetabular standard locking mechanism when there is a cross angle between metal cup and polyethylene liner. Simply textured at outer surface of the polyethylene liner to strengthen interface stability, and estimate the reinforce effect of the polyethylene-cemented interface. To evaluate the effect of cementing a polyethylene liner in the center of acetabular cup.3. To investigate the technical key points, feasibility and observe the early clinical effect of the technique that cementing a polyethylene liner into acetabular cup in hip revision.Methods1. Clinical investigation:32cases out of147patients(165hip) who were underwent THA in the First Affiliated Hospital of GuanZhou Medical College from January,1993to May,2006, have been performed Harris score by doctors and patients themselves, and the mean of which were compared by using pair-samples T test. Clinical retrospective analysis was performed in147patients (47male,80female) with a mean age60.2years (range,23-85years) who were underwent THA in the First Affiliated Hospital of GuanZhou Medical College before May2011. The anteroposterior films of pelvic were obtained by digital radiography in post-operation and follow-up to measure the abduction angle of acetabular cup by orthopedist and radiologist. Two groups of results were compared, and the incidence of excessive abduction angle greater than50°and55°were also calculated. Meanwhile, the linear polyethylene wear were measured on unilateral THA to access the correlation between abduction angle of acetabular cup and liner wear. Furthermore, the linear wear value of the polyethylene liner were compared between groups of abduction angle<50°and≥50degree, groups of using period less than5years and exceed5years.2. Biomechanical study:The lever-out test:25pair metal acetabular cups with polyethylene liners were randomly divided into5groups. One group with standard locking mechanism as control group, other liners were cemented into acetubular cups as experimental groups. According to the different intersection angle of metal acetabular cups with polyethylene liners and the polyethylene liners with/without metal ball, the four experimental groups were:no ball0degree group which is metal acetabular cups intersected with polyethylene liners(without metal ball) at0degree angle,0degree group which is metal acetabular cups intersected with polyethylene liners(with metal ball) at0degree angle,10degrees group which is metal acetabular cups intersected with polyethylene liners(with metal ball) at10degree angle,20degrees group which is metal acetabular cups intersected with polyethylene liners(with metal ball) at20degree angle. In order to obtain an even thickness of cement mantle, four balls of2mm diameter were placed between metal cup and polyethylene liner when liners were cemented. The lever-out biomechanical test was then performed at each group to evaluate the lever-out failure strength of liner-cement-metal cup interface. The torsion test:other25pairs metal acetabular cups with polyethylene liners were also randomly divided into5group. One group with standard locking mechanism group as control group, the others were prepared to imitate cementd liner technique as experimental groups. According to the different intersection angle of metal acetabular cups with polyethylene liners and the polyethylene liners with or without metal ball, four experimental groups were:non-ball0degree group stood for metal acetabular cups intersected with polyethylene liners(without metal ball) at0degree angle,0degree group stood for metal acetabular cups intersected with polyethylene liners(with metal ball) at0degree angle,10degrees group which is short for metal acetabular cups intersected with polyethylene liners(with metal ball) at10degree angle,20degrees group stood for metal acetabular cups intersected with polyethylene liners(with metal ball) at20degree angle. In order to obtain a uniform thickness of cemented shell, four balls of2mm in diameter were placed between metal cup and polyethylene liner while fixate liner with cement. The torsion test was also performed at each group to determine the anti-torsion strength of the liner-cement-metal cup interface. Texture reinforce test:10holes were made at the outer surface of5polyethylene liner (2symmetrical holes for each liner) by drill of3mm in depth. Therefore the polyethylene liner was interlocked with cement mantle after cement filled into the hole. Then the ant-torsion strength of the textured liner-cement-metal cup interface were tested and evaluated by comparing with the ant-torsion strength of the standard locking mechanism group.3. Cementing polyethylene liner into acetabular cup was performed in hip revision in two cases, and a short-term follow-up was carried out to get clinical and imaging findings.Results1. The clinical investigation results:In the final follow up, the mean Harris score evaluated by doctors was90.01±7.75points (range,68.5～100points), while take out the score of physical sign and action range, the mean Harris score was83.39+7.591points (range,62～91points) evaluated by doctors VS84.36+6.974points (range,66～91points) evaluated by patients themselves. No significant difference was found between the two groups(t=-0.1567, P=0.126). The mean acetabular abduction angle was47.56°±8.826°measured by joint surgeon VS48.41°±9.395°measured by radiologist, there was statistical difference (t=2.978, P=0.003). Out of145THA, there were32acetabular metal cups with an abduction angle greater than55degrees (15.3%～28.9%), and61acetabular metal cups with an abduction angle greater than50degrees (34.1%～50.1%). The mean of linear wear of polyethylene liner in107patients with unilateral THA was0.832±0.7069mm.A scatter diagram was made to reveal the relationship between abduction angle and liner wear in107unilateral THA, and then a curve estimation was taken by SPSS13.0. R square was up to0.697using Quadratic curve. Regression equation was y=4.431-0.21x+0.003x2.2. The results of lever-out test:loading on the same moment arm, the mean±sem liver-out failure force were respectively:non-ball0degree group,915.04±197.49N;0degree group,449.02±119.78N;10degrees group,814.68±53.89N; and20degrees group,1033.05±226.44N; while the standard locking group,626.68+206.12N. ANOVA showed significant difference between each mean lever-out force(F=8.989, P<0.001). The lever-out failure forces of20degrees group,10degrees group, non-ball0degree group, were greater than the standard locking group. Using LSD method, the standard locking control group as a control group were compared with each group, the standard locking control group VS20degrees group (P=0.001), VS non-ball0degree group(P=0.016), the mean lever-out failure force of20degrees group and no ball0degree group were significantly greater than the the standard locking control group(P<0.05); while the the standard locking control group VS10degrees group (P=0.102), VS0degree group(P=0.121), the lever-out failure forces were no statistically significant difference between the two groups. The results of torsion test:the mean±sem torsion failure torque were respectively:non-ball0degree group,6.39±1.03Nm;0degree group,7.60±1.73Nm;10degree group,7.01+2.25Nm;20degree group,7.32±1.56Nm; the standard locking group,23.82±3.78Nm. ANOVA showed significant difference between each mean torsion torque(F=50.859, P<0.001). Using Games-Howell method, the standard locking control group were compared with each group, the mean torsion failure torque of the standard locking control group were significantly greater than every experimental group (P=0.001), but no statistically significant difference was found between any two of the experimental groups. Texture reinforce results:the mean torsion torque were:the textured liner group,31.03±1.58Nm; the standard locking control group,23.82±3.78Nm. Using independent sampler T-test, the mean torsion torque were compared between two groups, and the mean torsion torque of the textured liner group was significant greater than the standard locking control group(t=-3.94, P=0.01).3. The Harris score of two cases were improved respectively from53,66before operation to97,97.5at final follow up, the operative result was satisfactory, no complication was find, the allograft bone was replaced well by new bone, meanwhile, no acetabular cup loosening and new osteolysis area were detected in the radiograms of pelvis and hip joint. Conclusion1. Harris score can be used as a clinical questionnaire, it was a helpful supplementary for clinical follow-up. The incidence rate of excessive abduction acetabular cup were relatively high in THA, the excessive abduction angle of acetabular cup was positively correlative to linear wear of polyethylene liner,and the excessive abduction of acetabular cup should be avoided in primary THA for which was relative to wear of polyethylene liner. The incidence rate of metal acetabular cup with should not be ignored due to the high rate of excessive abduction acetabular prosthesis, if the retroversion of acetabular prosthesis which was not measured in the study was take into consideration, the incidence rate of malposition metal acetabular cup will be increased. The feasibility and reliability of the technique that cemented polyethylene liner with correct direction into a stable but improper orientation metal acetabular cup were still need a further study.2. Comparing to standard locking mechanism, cementing a liner into a metal cup has similar resist strength to lever-out force, but less resist strength to torsion result from the sooth outer surface of polyethylene liner without texture, therefore, interface reinforcement by texture at the outer surface of polyethylene liner were need to improve the resist strength to torsion. The management of simple texture at the outer surface of the polyethylene liner can increase ant-torsion strength of the liner-cement interface, the interface fixation strength were also slightly better than the standard locking mechanism. The simple texture way at the outer surface of the polyethylene liner used in the study can be consulted to the design of new polyethylene liner.3. Bone cement polyethylene liner technique is feasible, effective and simple. Comparing to total acetabular revision, it is less trauma, recoverying quickly, retaining more bone mass of acetabulum, delaying the total acetabular revision acetabular revision surgery, so it is an alternative technique for acetabular revision.The main innovative pointsThe technical concept of cemented liner direction-adjusting was firstly proposed to cement a new liner in a correct direction into a stable but unsatisfied-directional metal acetabular cup, the interface strength were firstly evaluated in biomechanical test. In our knowledge, these are not reported in literature. |
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