Introduction

Current methodologies for designing and validating existing THA systems can be expensive and time-consuming. A validated mathematical model provides an alternative solution with immediate predictions of contact mechanics and an understanding of potential adverse effects. The objective of this study is to demonstrate the value of a validated forward solution mathematical model of the hip that can offer kinematic results similar to fluoroscopy and forces similar to telemetric implants.

Contemporary crosslinked polymers didn't just happen. The material was, has, and continues to be studied more than any other bearing surface material used in the total hip and total knee replacement construct. Historical failures and successes provided the information needed to make it the success that it is today as we approach the end of the second decade of extensive use.

Recognition that wear particles, not cement, was the major cause of osteolysis was important. Next, understanding that oxidation from free radical formation was deleterious to wear resistant polyethylene was understood and finally, that crosslinking was responsible for magnitude increases in wear resistance.

Although manufacturers have developed multiple processes to develop their crosslinked polymers (gamma and e beam radiation, melting and annealing, and most recently the addition of antioxidants) there are excellent 10-year results demonstrating head penetration rates (indicative of wear and creep) in the 0.02 to 0.04 mm/year range for many materials with minimal if any detection of osteolysis on radiographs and close to 0% revised for wear at 10+ years.

Are there any cautions? Recently, at 10- to 15-year follow up, some clinically insignificant osteolysis has been noted in one study and in that same study, 36 mm heads had twice the volumetric wear as 32 mm heads, but it was still a relatively low volume compared to the previous generation polyethylenes. We need further follow up, but at two decades of use, crosslinked polymers have dramatically reduced the osteolysis problem.

Successful nonarthroplasty solutions for the treatment of osteonecrosis of the femoral head continued to be sought. However, no definitive nonarthroplasty solutions have to date been found. Hence, even in the best of hands a large number of patients with osteonecrosis end up with debilitating end-stage osteoarthritis.

In the inception of total hip arthroplasty (THA), the results of treatment of femoral head osteonecrosis by THA were inferior to total hip replacement performed for osteoarthritis. Reasons for this included the young age of many osteonecrosis patients, the high numbers of comorbidities in this population (SLE, sickle cell anemia, alcoholism), and the poor bone quality at the time of surgery. Arthroplasty considerations included bipolar replacement, hemiresurfacing, resurfacing (non metal-on-metal and later metal-on-metal), cemented total hip arthroplasty and cementless total hip arthroplasty. Previous to the use of cementless arthroplasty, all of these procedures had a relatively high 5 to 10 year failure rate of 10–50%. Even our own 10-year results using contemporary cementing techniques demonstrated 10% failure compared to 1–2% failure in our nonosteonecrosis patients. For this reason, it made sense to continue exploring nonarthroplasty solutions for osteonecrosis of the hip.

The introduction of cementless fixation for total hip arthroplasty changed the entire thinking about hip osteonecrosis treatment for many of us. Although initially we were concerned about whether bone would grow into the prosthesis in the environment of relatively poor bone, the early results demonstrated that it can and does. Most recently, with the use of crosslinked polyethylene, the cementless construct gives many of us hope that with cementless fixation, the treatment of many patients including the young (especially if followed closely to exchange bearing surfaces if necessary) will last a lifetime with THA being the only and definitive procedure. Our most recent 10-year results demonstrated a femoral stem revision rate of 1.5% will all other stems (other than the stem revised) bone ingrown. Acetabular fixation was also 100% and although 6% required liner exchange, our own and others' results with crosslinked polyethylene would suggest that this problem should be markedly reduced.

Introduction

Fracture around the knee can lead to posttraumatic osteoarthritis (PTOA) of the knee. Malunion, malalignment, intra-articular osseous defects, retained internal fixation devices, and compromised soft tissues may affect the outcome of total knee replacement (TKR). On average, the posttraumatic patient subsets were 10.4 years younger than those for primary knee OA. Recently, there were several studies reporting the outcome of THA for posttraumatic OA hip. However, no current literature defines the comparative functional outcome between PTOA and primary OA knee.

The purpose of our study was to compare the midterm outcomes of patients undergoing TKR following periarticular knee fractures/ligamentous injuries versus primary osteoarthritis (PO) of the knee.

Background

Readmission following any total joint arthroplasty has become a closely watched metric for many hospitals in the United States because financial penalties imposed by CMS for excessive readmissions occurring within thirty days of discharge has occurred since 2015. The purpose of this study was to identify both preoperative comorbidities associated with and postoperative reasons for readmission within thirty days following primary total joint arthroplasty in the lower extremity.

Liner exchange and bone grafting are commonly used in cases of wear and osteolysis around well- fixed acetabular components in revision total hip arthroplasty. However, in total knee revision, liner exchange is a more rare option.

In a multicenter study, we evaluated 22 TKAs that were revised with liner exchange and bone grafting for wear and osteolysis. All knees were well-fixed and well-aligned, and all components were modular tibial components. Osteolytic areas averaged 21.1cm2 and 7.6cm2 on AP projections of the femur and tibia, respectively, and averaged 21.6cm2 and 5.7cm2 on lateral projections of the femur and tibia, respectively, with the largest area being 54cm2 on a single projection. Follow up was minimum 2 years and average 40 months. No knees were revised and radiographically, all osteolytic lesions showed evidence of complete or partial graft incorporation. In addition, there was no radiographic evidence of loosening at final follow up.

The Mayo Clinic evaluated 56 isolated tibial insert exchange revisions at their institution. Cases of loosening, infection, knee stiffness, or extensor mechanism problems were excluded. At minimum 2-year follow up (average 4.6 years), 14 knees (25%) required re-revision.

Baker et al. evaluated 45 total knees undergoing isolated tibial insert exchange. At minimum 2 years, 4 knees (9%) required revision. Significant improvement was seen in clinical outcomes questionnaires, but only 58% had clinical successful global WOMAC scores.

In summary, isolated liner exchange in the revision total knee setting has variable results. It can be successful but it is indeed a rare option and should be limited to cases were the total knee arthroplasty is both well-fixed and well-aligned.

There are several clinical scenarios to consider cementing an acetabular liner into a secure cementless shell including cases of: 1) inadequate capturing mechanism, 2) damaged locking mechanisms, 3) unavailability of the mating polyethylene liner, 4) instability following debridement for wear, 5) instability at the time of femoral side revision, and 6) recurrent dislocation. The last two situations are common scenarios for cementing a constrained liner into a secure shell.

Technique includes: 1) scoring the shell in cases with no screw holes or polished inner shells, 2) scoring the acetabular liner in a “spider web” pattern, 3) pressurizing cement into the shell, and 4) inserting a liner that allows 2mm of cement mantle.

Results of Cementing Constrained Liner Into Secure Cementless Shell: Callaghan et al. JBJS 2004. Thirty-one hips at 2–10 year follow-up. Two of 31 failed. Technical considerations: do not cement proud and do not cement into a malpositioned shell; Haft et al. J Arthroplasty 2002. Seventeen hips with minimum 1 year follow-up. One of 17 failed. Technical considerations: do not cement proud.

Results of Cementing Non-Constrained Liners Into Secure Cementless Shell: Beaule et al. JBJS 2004. Thirty-two hips at mean 5.1 year avg f/u. Four components revised for loosening; Callaghan et al. CORR 2012. Thirty-one hips at mean 5.3 year f/u. No revisions.

In primary total hip replacements there are numerous options available for providing hip stability in difficult situations (i.e. Down's syndrome, Parkinson's disease). We have considered constrained liners in some of these cases.

However, in the revision situation in general and in revision for recurrent dislocation situation specifically it is important to have all options available including tripolar constrained liners in order to optimise the potential for hip stability as well as function of the arthroplasty. Even with the newer options available dislocation rates of higher than 10–15% have been reported following revision surgery at institutions where high volumes of revision surgery are performed. Because of the deficient abductors, other soft tissue laxity and the requirement for large diameter cups revision cases will always have more potential for dislocation. In these situations in the lower demand patient, constraint has provided excellent success in terms of preventing dislocation and maintaining implant construct fixation to bone at intermediate- term follow-up. Hence in these situations tripolar constrained liners remains the option we utilise. We are also confident in using this device in cases with instability or laxity where there is a secure well- positioned acetabular shell. We cement a dual mobility constrained liner in these situations using the technique described below.

Present indication for tripolar constrained liners: low demand patient, large outer diameter cups, instability with well-fixed shells that are adequately positioned, abductor muscle deficiency or soft tissue laxity, multiple operations for instability

Technique of cementing liner into shell: score acetabular shell if no holes, score liner in spider web configuration, all one or two millimeters of cement mantle

Significant hip osteoarthritis has been reported in 8–28% of patients with Down Syndrome. The prolonged life expectancy of these patients has allowed many of them to become disabled by their hip arthritis with the need for hip replacement.

We have been able to perform a multi-center study evaluating total hip replacement in patients with Down Syndrome. Twenty patients (25 hips) with Down Syndrome underwent primary THA at a mean age of 35 years old with a mean 105-month follow-up. Cementless acetabular fixation with screws were used in all cases and all but one femoral component was cementless. Constrained liners were used in 8 cases to enhance stability. Five hips required revision surgery: two femoral components (one for periprosthetic fracture and one for aseptic loosening), two acetabular components (one for recurrent dislocation and one for wear with metallosis), and one hip required a two-stage revision for infection. Other than the hip revised for loosening, no other hip had radiographic evidence of loosening. The mean Harris Hip score improved from 42 points pre-operatively to 83 points at final follow-up.

THA is a reliable surgical intervention in patients with Down Syndrome and symptomatic coxarthrosis. These patients and their families have been tremendously satisfied with this procedure. Strategies to prevent dislocation post THA are appropriate and need continued evaluation.

Total knee arthroplasty has been demonstrated to provide durable results with excellent pain relief and improvement in function. Our institution has studied and published the longest follow-up of mobile bearing TKR, fixed bearing modular TKR, and unicompartmental replacement. Indeed these studies support the durability of the operation and the improvement in function and relief of pain. They, however, are not perfect. In tricompartmental replacement, up to 5 or 6% are revised for loosening and or wear and in unicompartmental replacement, up to 25% are revised for loosening. There are also one or two percent of cases revised for periprosthetic fracture and one or two percent for hematogenous infection. One must remember these cases were performed in patients of average age 71.

When one looks at our results in more active patients with osteoarthritis who are less than 55, the results are less spectacular with 15% revised at 10 to 15 years for loosening. We all hope that better polyethylene and better tibial tray locking mechanisms (in fixed bearing modular designs) will improve these results, but to predict there will be no failures is a “leap of faith”. Long-term follow-up of cemented TKA in patients under 55 where monolithic tibial trays were utilised have demonstrated better results at 20 years (92.3%) survivorship versus those where modular tibial trays (68%) were utilised. Long-term studies of cementless total knee replacement, especially in younger patients are needed to see if this approach provides better results.

The United States is in the midst of an opioid epidemic, with the World Health Organization reporting that American's consume 99% of the world's supply of hydrocodone and 83% of the world's oxycodone. Additionally, pre-operative opioid use has been associated with worse clinical outcomes and higher rates of complications following TKA. This is especially important in the TKA population given that approximately 15% of patients are either dissatisfied or very dissatisfied at least one year after their TKA procedure. Given the concerning rise is opioid use the American Academy of Orthopaedic Surgeons (AAOS) has recently released an information statement with practice recommendations for combating this excessive and inappropriate opiate use. However, little is known regarding peri-operative opioid use for TKA patients. Therefore, the purpose of this study was to: 1) identify rates of opioid use prior to primary TKA, 2) evaluate post-operative trends in opioid use throughout the year following TKA and 3) identify risk factors for prolonged opioid use following TKA.

Overall, 31% of TKA patients are prescribed opioids within 3-months prior to TKA; this percentage has increased over 9% during the years included in this study. Pre-operative opioid use was most predictive of increased refills of opioids following TKA, however, other intrinsic patient characteristics were also predictive of prolonged opioid use. These characteristics remained predictive after controlling for opioid user status. The increasing rates of opioid prescribing prior to TKA are concerning, especially given literature concluding opioids have minimal effect on pain or function in patients with osteoarthritis and pre-operative opioid use is associated with poor outcomes and more complications following TKA. This data provides an important baseline for opioid use trends following TKA that can be used for future comparison and identifies risk factors for prolonged use that will be helpful to prescribers as the AAOS works to decreased opioid use, misuse and abuse within the United States. Our data on THA and unicompartmental arthroplasty is similar with an increase in pre-THA use of 9% with 38% receiving narcotics within 3 months of surgery and continued use in opioid users (9 times non-opioid users at 12 months).

Background

Readmission following any total joint arthroplasty has become a closely watched metric for many hospitals in the United States because financial penalties imposed by CMS for excessive readmissions occurring within thirty days of discharge will be forthcoming in 2015. The purpose of this study was to identify both preoperative comorbidities associated with and postoperative reasons for readmission within thirty days following primary total joint arthroplasty in the lower extremity.

Three basic design concepts of cementless femoral fixation have emerged. They include: anatomic designs, straight stem designs, and tapered designs. In addition, there have been modular designs. The most successful have been designs that have a metaphyseal sleeve with a tapered stem. A more recent newer concept has been the double taper neck designs which have not performed well in general.

Anatomic Stem Designs: The rationale for an anatomic stem design was to design a component that matched the sagittal plane bow of the femur. The APR (Centerpulse, Austin, Texas) and the PCA (Howmedica, Rutherford, New Jersey) were the initial designs. Although these designs provided excellent micromotion stability, they are not used in their present length today because they could not fit in to all femurs.

Straight Stem Designs: The concept of a straight stem design was to machine the femur to accept the prosthesis. This was done with diaphyseal reaming, proximal broaching, and preparing a proximal triangle to accommodate the proximal metaphyseal portion of the stem. These had previously, and still do, come in proximally coated and distally coated designs. They have proven to be durable long term. The AML fully coated stem (DePuy, Warsaw, Indiana) was and still is the prototype device.

Tapered Stem Designs: The most popular designs today are the tapered stems. They are inserted either by a broach only, or ream and broach technique. Some only taper in the ML plane and are flat in the AP plane. These are called ML taper or blade devices (Taperloc and Trilock). These are usually inserted broach only. Some have a double taper with proximal fill and include the Zweymuller stem (Zimmer, Warsaw, Indiana), the Omnifit stem (Stryker, Mahwah, New Jersey), the Summit stem, and the Corail stem (both DePuy, Warsaw, Indiana). Some are hydroxyapatite coated (Omnifit and Corail), some are porous coated (Summit), and some are only grit blasted (Zweymuller). Some are broach only including the Zweymuller and Corail, and some are broach and ream including the Omnifit and Summit. Some are tapered throughout, one of which is a Wagner type design, Trilogy (Zimmer, Warsaw, Indiana). These Wagner type devices are useful in abnormal anatomy (CDH and Perthes).

Modular Stem and Dual Modular Neck Designs: Metaphyseal sleeve modular stem designs are extremely versatile and can be inserted press fit into just about any femoral anatomy. They are most commonly utilised in cases of hip dysplasia with marked femoral anteversion. The S-ROM device is the prototype design. The long term concern with these as well as the double neck tapered devices is fretting and corrosion at the extra modular junctions.

Short Stem Designs: Short stem designs were developed to provide metaphyseal only fixation and to enable easy insertion through small incision techniques, especially those performed through anterior and antero-lateral approaches.

In the revision situation in general and for recurrent dislocation specifically, it is important to have all options available including tripolar constrained liners in order to optimise the potential for hip stability as well as function. Even with the newer options available, dislocation rates of higher than 5% have been reported in the first two years following revision surgery at institutions where high volumes of revision surgery are performed (Wera et al). Because of the deficient abductors, other soft tissue laxity and the requirement for large diameter cups, revision cases will always have more potential for dislocation. In these situations, in the lower demand patient, tripolar constrained liners provided excellent success in terms of preventing dislocation and maintaining implant construct fixation to bone at intermediate term follow-up. Hence in these situations, tripolar with constraint remains the option we utilise in many cases. We are also confident in using this device in cases with instability or laxity where there is a secure well positioned acetabular shell. We cement a tripolar constrained liner in these situations using the technique described below.

Present indication for tripolar constrained liners: low demand patient, abductor muscle deficiency or soft tissue laxity, large outer diameter cups, multiple operations for instability, instability with well-fixed shells that are adequately positioned

Technique of cementing liner into shell: score acetabular shell if no holes, score liner in spider web configuration, all one or two millimeters of cement mantle

Results: Constrained Tripolar Liner - For Dislocation: 56 Hips; 10 year average f/u; 7% failure of device, 5% femoral loosening, 4% acetabular loosening

Constrained Tripolar Liner - For Difficult Revisions: 101 hips; 10 year average f/u; 6% failure of device, 4% femoral loosening, 4% acetabular loosening

Cementing Liner into Shell: 31 hips; 3.6 year average f/u (2–10 years); 2 of 31 failures

We, like others, are trying to define cases where dual mobility will be as successful or more successful than tripolar constrained liners.

Liner exchange and bone grafting are commonly used in cases of wear and osteolysis around well fixed acetabular components in revision total hip arthroplasty. However, in total knee revision, liner exchange is a more rare option.

In a multicenter study, we evaluated 22 TKAs that were revised with liner exchange and bone grafting for wear and osteolysis. All knees were well fixed and well aligned, and all components were modular tibial components. Osteolytic areas averaged 21.1 cm2 and 7.6 cm2 on AP projections of the femur and tibia, respectively, and averaged 21.6 cm2 and 5.7 cm2 on lateral projections of the femur and tibia, respectively, with the largest area being 54 cm2 on a single projection. Follow up was minimum 2 years and average 40 months. No knees were revised and radiographically, all osteolytic lesions showed evidence of complete or partial graft incorporation. In addition, there was no radiographic evidence of loosening at final follow up.

The Mayo Clinic evaluated 56 isolated tibial insert exchange revisions at their institution. Cases of loosening, infection, knee stiffness, or extensor mechanism problems were excluded. At minimum 2 year follow up (average 4.6 years), 14 knees (25%) required re-revision.

Baker et al evaluated 45 total knees undergoing isolated tibial insert exchange. At minimum 2 years, 4 knees (9%) required revision. Significant improvement was seen in clinical outcomes questionnaires, but only 58% had clinical successful global WOMAC scores.

In summary, isolated liner exchange in the revision total knee setting has variable results. It can be successful but it is indeed a rare option and should be limited to cases where the total knee arthroplasty is both well fixed and well aligned.

Introduction: I always aim for neutral mechanical axis alignment. My principles of a successful TKA are proper alignment in all 3 planes, soft tissue balance in extension first, flexion gap balancing by parallel to tibial cut technique, maintenance of joint line, correct sizing of femoral component, and proper cement fixation.

Long-term Survivorship: There is long-term data that supports the efficacy and durability of the neutral position of proximal tibial cut. Over a 20-year follow-up there was a 92.6% success rate in my study. Other authors have found similarly successful survivorship for mechanical failure.

Balance Technique in TKR: My technique to balance the knee is a balance extension gap first, which requires medial soft tissue balancing. Next, I balance the flexion gap parallel to the tibial cut.

Our Results: In one study, I examined the clinical and radiographic data of 68 varus knees. Average post-operative mechanical alignment was 0 ± 3 degrees. There were no outliers which displays the reproducibility of the technique. This is the method of choice in the hands of most surgeons.

In primary total hip replacements there are numerous options available for providing hip stability in difficult situations (i.e. Down's syndrome, Parkinson's disease).

However, in the revision situation in general and in revision for recurrent dislocation specifically, it is important to have all options available including dual mobility constrained liners in order to optimise the potential for hip stability as well as function of the arthroplasty. Even with the newer options, available dislocation rates of higher than 5% have been reported in the first two years following revision surgery at institutions where high volumes of revision surgery are performed. Because of the deficient abductors, other soft tissue laxity and the requirement for large diameter cups, revision cases will always have more potential for dislocation. In these situations in the lower demand patient and where, a complex acetabular reconstruction that requires time for ingrowth before optimal implant bone stability to occur isn't present, dual mobility with constraint has provided excellent success in terms of preventing dislocation and maintaining implant construct fixation to bone at intermediate term follow-up. Hence in these situations dual mobility with constraint remains the option we utilise. We are also confident in using this device in cases with instability or laxity where there is a secure well-positioned acetabular shell. We cement a dual mobility constrained liner in these situations using the technique described below.

Present indication for dual mobility constrained liners: low demand patient, large outer diameter cups, instability with well-fixed shells that are adequately positioned, abductor muscle deficiency or soft tissue laxity, multiple operations for instability

Technique of cementing liner into shell: score acetabular shell if no holes, score liner in spider web configuration, all one or two millimeters of cement mantle

Results: Constrained Dual Mobility Liner – For Dislocation: 56 Hips, 10 year average follow-up, 7% failure of device, 5% femoral loosening, 4% acetabular loosening. For Difficult Revisions: 101 hips, 10 year average follow-up, 6% failure of device, 4% femoral loosening, 4% acetabular loosening. Cementing Liner into Shell: 31 hips, 3.6 year average follow-up (2–10 years), 2 of 31 failures.

The United States is in the midst of an opioid epidemic, with the World Health Organization reporting that American's consume 99% of the world's supply of hydrocodone and 83% of the world's oxycodone. Additionally, pre-operative opioid use has been associated with worse clinical outcomes and higher rates of complications following total knee arthroplasty (TKA). This is especially important in the TKA population given that approximately 15% of patients are either dissatisfied or very dissatisfied at least one year after their TKA procedure. Given the concerning rise in opioid use the American Academy of Orthopaedic Surgeons (AAOS) has recently released an information statement with practice recommendations for combating this excessive and inappropriate opiate use. However, little is known regarding peri-operative opioid use for TKA patients. Therefore, the purpose of this study was to: 1) identify rates of opioid use prior to primary TKA, 2) evaluate post-operative trends in opioid use throughout the year following TKA and 3) identify risk factors for prolonged opioid use following TKA.

Overall, 31% of TKA patients are prescribed opioids within 3-months prior to TKA; this percentage has increased over 9% during the years included in this study. Pre-operative opioid use was most predictive of increased refills of opioids following TKA, however, other intrinsic patient characteristics were also predictive of prolonged opioid use. These characteristics remained predictive after controlling for opioid user status. The increasing rates of opioid prescribing prior to TKA are concerning, especially given literature concluding opioids have minimal effect on pain or function in patients with osteoarthritis and pre-operative opioid use is associated with poor outcomes and more complications following TKA. This data provides an important baseline for opioid use trends following TKA that can be used for future comparison and identifies risk factors for prolonged use that will be helpful to prescribers as the AAOS works to decreased opioid use, misuse and abuse within the United States.

Moderately to highly crosslinked UHMWPEs have functioned for at least a decade with dramatic reduction in wear volumes in THA. This wear reduction has been associated with a markedly reduced incidence of radiographic osteolysis. However, CT studies have demonstrated that osteolysis is not completely eliminated.

There, however, are still questions which include: Is cost for further improvements warranted?; Is 10 years long enough to assure that no clinically relevant osteolysis occurs, especially in younger patients?; Do we have any data demonstrating improvement in revision scenarios?; With high levels of crosslinking (requiring more radiation) some fractures have been demonstrated at the region of the locking mechanism of the liner to shell. Will this prevalence increase? These materials are softer and can cause quicker crack propagation than conventional polyethylene.; Do better locking mechanisms need to be developed to prevent fracture problems that have been demonstrated in the present generation cementless designs?; Do we need more information as to the optimal counterface choice (cobalt chrome, ceramic, oxinium)?; Can hip results be extrapolated to the knee where fatigue failure is a major problem both on the bearing surface and with the locking mechanism?; Is the oxidation we are beginning to see on the surface of retrieved liners (thought to be related to lipids from the synovium and cyclical loading) the tip of the iceberg?

I too am encouraged by the mid-term results of crosslinked polyethylene. Our own data supports it. However, we must keep in mind the questions outlined.

In primary total hip replacements there are numerous options available for providing hip stability in difficult situations i.e. Down's syndrome, Parkinson's disease. However, in the revision situation, in general, and in revision for recurrent dislocation situations specifically, it is important to have all options available including dual mobility constrained liners in order to optimise the potential for hip stability as well as function of the arthroplasty. Even with the newer options available dislocation rates of higher than 5% have been reported in the first two years following revision surgery at institutions where high volumes of revision surgery are performed [Della Valle, Sporer, Paprosky unpublished data]. Because of the deficient abductors, other soft tissue laxity and the requirement for large diameter cups, revision cases will always have more potential for dislocation. In these situations in the lower demand patient and where, a complex acetabular reconstruction that requires time for ingrowth before optimal implant bone stability to occur isn't present, dual mobility with constraint has provided excellent success in terms of preventing dislocation and maintaining implant construct fixation to bone at intermediate term follow-up. Hence in these situations dual mobility with constraint remains the option we utilise. We are also confident in using this device in cases with instability or laxity where there is a secure well-positioned acetabular shell. We cement a dual mobility constrained liner in these situations using the technique described below.

Present indication for dual mobility constrained liners: low demand patient, abductor muscle deficiency or soft tissue laxity, large outer diameter cups, multiple operations for instability, and instability with well-fixed shells that are adequately positioned.

Technique of cementing liner into shell: score acetabular shell if no holes; score liner in spider web configuration; all one or two millimeters of cement mantle.