Introduction

The importance of frontal and rotational alignment in total knee arthroplasty has been published. Together with conventional instrumentation, computer navigation has been used for many years now. The pro's and con's of navigation are well known since.

Component and limb alignment are important considerations during Total Knee Arthroplasty (TKA). Three-dimensional positioning of TKA implants has an effect on implant loosening, polyethylene stresses, and gait. Furthermore, alignment, in conjunction with other implant and patient variables such as body mass index (BMI) influence osseous loading and failure rates. Fortunately, implant survivorship after TKA has been reported to be greater than 95% at 20 years, despite up to 28% of TKAs having component position greater than 3 degrees from neutral. How good are we at positioning TKA implants with standard instrumentation? Ritter, et al examined 6,070 primary TKAs and found that from 2 degrees – 7 degrees of valgus, the failure rate was 0.5% for limb alignment. Importantly 28% of the TKAs were outside the 2 degrees – 7 degrees range in the hands of experienced surgeons. What about cases with retained hardware or deformities that preclude IM or EM guides.

Clearly there is room for improvement in surgical technique, but this improvement must be (1) time efficient and cost effective; (2) have a low complication rate, and (3) be reproducible with a minimal learning curve. One of the technologies that has been developed to help surgeons implant and position TKA components is a patient matched guide. Preoperative computerised planning of the arthroplasty, development of patient specific guides, combined with limited mechanical instruments has been a significant step forward for the surgeon and patient.

“The logistical benefits include possible decreased operating room time, decreased turnover time, less time spent sterilising and preparing trays, less inventory, less strain on surgical technicians and nurses, and no capital cost associated with computer navigation. Patient benefits include potentially less tourniquet time, less surgical exposure, no requirement of intramedullary canal preparation, and improved mechanical alignment, which may translate to increased implant longevity. Surgeon benefits include potentially more accurate landmark registration than computer navigation, more efficient surgery, decreased intraoperative stress due to less required decision making, and the ability to perform more surgeries due to time saved.”

Ng, et al compared 569 TKAs performed with patient-specific positioning guides and 155 with manual instruments. The overall mean hip-knee-ankle angle for patient-specific positioning guides (180.6 degrees) was similar to manual instrumentation (181.1 degrees), but there were fewer ± 3 degrees hip-knee-ankle angle outliers with patient-specific positioning guides (9%) than with manual instrumentation (22%).

Patient-specific instruments for total knee arthroplasty shift the bone landmark registration and implant positioning of computer navigation from intraoperative to the pre-operative setting. A preoperative MRI or CT scan is mandatory, with the specifications determined by the instrument manufacturer. Default implant sizing and alignment targets must be templated by the surgeon and mapped onto the virtual knee. The surgeon must also review and modify the preoperative computer plan to incorporate any clinical findings, such as flexion contracture or fixed deformity. The finalised preoperative plan is sent back to the implant vendor for fabrication of patient-specific cutting blocks in 4–6 weeks. The supposed advantages of these instruments include more accurate coronal alignment, fewer outliers, no instrumentation of intramedullary canal, decreased operative time, and decreased hospital costs to clean-sterilise instruments. There are many disadvantages of patient-specific instruments, including: cost, preoperative scheduling of imaging, the learning curve for the surgeon, and the uncalculated preoperative planning time. A set of conventional instruments should be available if the custom instruments do not fit properly. One study of 66 knees using PSI reported that frequent surgeon-directed changes were required, 2.4 per knee, implant sizes were changed in 77% of femurs and 53% of tibias, and tourniquet time was not improved. A Markov model study reported an increased cost of $4600 for 4.6 QALYs for patient-specific instruments and that the rate of revision must be reduced by 50% or more for these instruments to be cost-effective. There is little evidence to support the claims made by the manufacturers of these instruments. We advise against the widespread use of these instruments for total knee arthroplasty.

Summary Statement

A prospective randomised evaluation of primary TKA utilizing patient specific instruments demonstrated great accuracy of bone resection, improved sagittal alignment and the potential to improve functional outcomes and reduce operating room costs when compared to standard TKA instrumentation.

Total Knee Artroplasty (TKA) is becoming more and more popular, even in the younger active age group. In this age group however the results are not that reproducible as in the older age group. People are more limited in their activities of daily living and complain more about pain, stifness and swelling. At the end and in general the younger age group is less satisfied than the older patients.

The last decade minimal invasive solutions with modified instruments, Gender Knees, the use of navigation in TKA, ligament-based techniques, fast rehab protocols etc have all been introduced to make the results of TKA better. These are all elements that indeed can make the patient better. However the most important on the short term and the long term is the use of the correct implant size and the correct implantation of the prosthetic components.

Since January 2011 we routinely use patient specific instruments in TKA patients under 60y that are very active or in older less active patients with important anatomic malformations. A CT-based system that scans the hip-knee-ankle is used. The data are sent to an engineer and a digital proposal is sent back to the surgeon that can approve the different measurements performed. Once approved the patient specific cutting blocks are sent to the surgeon. In our department we use the Advance Medial Pivot Knee System as our standard knee system since its introduction thirteen years ago. Since then more than 2000 implantations have been performed. This experience has made it possible to critically evaluate the patient specific cutting block technique.

The first results are very satisfying. During surgery less ligamentous releases had to be performed, there was in all cases an optimal patellofemoral tracking without any release, there was less blood loss and surgery time was decreased. At all times during surgery we were very satisfied how we could verify all surgical steps and this is in our opinion very important. During the first postoperative days the patients experienced less pain (routine VAS recorded), there was a faster return to full ROM and patients asked to go home earlier.

After two months patients are routinely followed up and they undergo a clinical and radiographic exam. All prosthetic components were implanted the way we had planned it. The overall axes were restored and up till now no complications were noticed. All patients experienced a fast recovery with full ROM at 2 months, no complaints about pain or swelling and very interestingly no residual intra-articular swelling which is often seen in these active and younger patient group. Patients are also asked to fill in a patient-based outcome measurements (KOOS) questionnaire.

In our opinion it is a very easy and promising system for the experienced surgeon. Younger and less experienced surgeons however should be warned that they cannot blindly trust the system. We surgeons have to control what the engineer has proposed before and during surgery.

Purpose

Arthritis is the most common chronic illness in the United States. TKR provides reliable pain relief and improved function for patients with advanced knee arthritis. Total joint replacement now represents the greatest expense in the national healthcare budget. Surgical costs are driven by two key components: fixed and variable costs. Patient Specific Instruments™ (PSI, Zimmer, Warsaw, IN, USA) has the potential to reduce both fixed and variable costs by shortening operative time and reducing surgical instrumentation. However, PSI requires the added costs of pre-operative MRI scanning and fabrication of custom pin guides. Previous studies have shown reduction in operating room times and required instrumentation, but question the cost-effectiveness of the technology. Also, these studies failed to show improvement in coronal alignment, but call for additional studies to determine any improvement in clinical function and patient satisfaction. Our pilot study aims to compare the incremental PSI costs to fixed and variable OR cost savings, and compare meaningful patient and clinical outcomes between PSI and standard TKR surgeries.

Patient Specific Instruments (PSIs) are becoming increasingly common in arthroplasty but have only been used with highly invasive surgical approaches that can result in significant complications. We have previously described a novel PSI for minimally invasive total shoulder arthroplasty and shown that it can accurately guide the creation of guide holes in the humerus and scapula. However, conducting shoulder replacement in a minimally invasive environment precludes the use of traditional instruments. In this work, we describe and evaluate the efficacy of a set of novel instruments that, in conjunction with our PSIs, enable accurate minimally invasive total shoulder arthroplasty to be achieved for the first time. The key components of this surgical procedure are: 1) a new minimally invasive posterior surgical approach that avoids the need for muscle transection; 2) a novel PSI that enables accurate guide tunnels to be simultaneously created in the humerus and scapula using a c- shaped drill guide that mates to the PSI; 3) a custom humeral head resection guide that uses the humeral guide tunnel; 4) a novel reamer and 3D metal printed gear mechanism for radial displaced drilling both powered by a central driver placed through the humeral head; and 5) custom impactors for glenoid and humeral implantation – the latter is achieved using a modular slap hammer that is guided by the central humeral drill hole. Accuracy of this system was assessed at each surgical step using an optical tracking camera and an iterative closest point registration method to map measurements to the pre-operative plan. The accuracy results for the physical PSI registration and guide hole drilling were found to be in line with our previously reported results: the intra-articular guide hole locations were 2.2mm and 3.9mm for the humerus and glenoid with angular errors of 2.8° and 8°, respectively. After humeral resection, the humeral cut plane had an angular error of 10.1°. The final humeral implant location had an error of 12.1° and 1.9mm. For the glenoid implant, the positional error was 3.8mm with angular errors of 3.3° ante-retroversion and 8.6° supero- inferior inclination. We believe that these initial results demonstrate that this minimally invasive PSI and instrumentation system can accurately guide total shoulder replacement while avoiding the complications of open surgery. A full cadaveric testing series is currently being completed

Patient Specific Instruments (PSIs) are becoming an increasingly common method to provide surgeons with assistance in accurately performing procedures; however, to our knowledge, these new instruments have only been applied to traditional, highly invasive surgical approaches. However, PSIs have the potential to decreased surgical invasiveness by reducing the surgeon's need to clearly visualise anatomical landmarks. Therefore, we designed and evaluated a novel PSI for minimally invasive shoulder arthroplasty. The proposed minimally invasive approach prevents en face access to the articular surfaces and thus the PSI was designed to guide the accurate placement of a trans-humeral bone tunnel which would permit surgical steps to be conducted. To accurately create this tunnel and place a guide pin in the glenoid, the PSI was designed as a two sided guide that incorporates unique anatomical features from both bones, which would lock the two bones in a predefined pose relative to one another. Proper registration of the PSI is aided by the joint's passive compression force, which is not disrupted due to the soft tissue sparing approach. Once the bones are locked together, a guide pin could be passed through the humeral head – creating a bone tunnel to guide later humeral bone preparation – and into the glenoid to guide reaming and drilling. By designing the guide in this way, it is possible to avoid the need to perform surgical steps with a clear en face view. The PSI was created by loading 3D reconstructed CT models of the humerus and scapula into a CAD package, aligning the desired humeral and scapular guide axes such that the bones' relative pose is fully defined, and finally constructing the guide itself between and around the articular surfaces, such that sufficient anatomical features are incorporated to provide complete physical registration with the bones. This PSI was subsequently customised, based on a cadaveric specimen and fabricated using a 3D printer. The PSI's usability and accuracy in achieving the pre-operative plan were then assessed using optical tracking and surface based registration procedure. Results of the evaluation demonstrated that the designed PSI is capable of accurately registering the two bones to within 5mm and 14° of the intended pre-operative plan, while also effectively reducing the invasiveness of the surgical procedure. Therefore, this novel PSI may represent a new avenue to improve the clinical impact of CAOS systems, by achieving good surgical accuracy, but with a greatly reduced invasiveness

Background. Dislocation is a common complication after proximal and total femur prosthesis reconstruction for primary bone sarcoma patients. Expandable prosthesis in children puts an additional challenge due to the lengthening process. Hip stability is impaired due to multiple factors: Resection of the hip stabilizers as part of the sarcoma resection: forces acts on the hip during the lengthening; and mismatch of native growing acetabulum to the metal femoral head. Surgical solutions described in literature are various with reported low rates of success. Objective. Assess a novel 3D surgical planning technology by use of 3D models (computerized and physical), 3D planning, and Patient Specific Instruments (PSI) in supporting correction of young children suffering from hip instability after expandable prosthesis reconstruction following proximal femur resection. This innovative technology creates a new dimension of visualization and customization, and could improve understanding of this complex problem and facilitate the surgical decision making and procedure. Method. Two children, both patients with Ewing Sarcoma of the left proximal femur stage-IIB, ages 3/5 years at diagnosis, were treated with conventional chemotherapy followed by proximal femur resection. Both were reconstructed with expandable prosthesis (one at resection and other 4 years after resection). Hip migration developed gradually during lengthening process in the 24m follow up period. 3D software (Mimics, Materialise, Belgium) were used to make computerized 3D models of patients' pelvises. These were used to 3D print 1:1 physical models. Custom 3D planning software (MSk Lab, Imperial College London) allowed surgeons visualizing the anatomical status and assess of problem severity. Thereafter, osteotomies planes and the desired position of acetabular roof after reduction of hip joint were planned by the surgeons. These plans were used to generate 3D printed PSIs to guide the osteotomies during shelf and triple osteotomy surgeries. Accuracy of planning and PSIs were verified with fluoroscopy and post-op X-rays, by comparing cutting planes and post-op position of the acetabulum. Results. Surgeons reported excellent experience with the 3D models (computerized and physical). It helped them in the decision process with an improved understanding of the relationship between prosthesis head and acetabulum, a clear view of the osteophytes and bone formation surrounding the pseudoacetabulum, and osteophytes inside the native acetabulum. These osteophytes were not immediately visible on 2D CT imaging slices. Surgeons reported a good fit and PSIs' simplicity of use. The hip stability was satisfactory during surgery and in the immediate post-op period. X-ray showed a good and centered position of the hip and good levels of the osteotomies. Conclusions. 3D surgical planning and 3D printing was found to be very effective in assisting surgeons facing complex problems. In these particular cases neither CT nor MRI were able to visualize all bony formation and entrapment of prosthesis in the pseudoacetabulum. 3D visualisation can be very helpful for surgical treatment decisions, and by planning and executing surgery with the guidance of PSIs, surgeons can improve their surgical results. We believe that 3D technology and its advantages, can improve success rates of hip stability in this unique cohort of patients

The aim of this project is to test the parameters of Patient Specific Instruments (PSIs) and measuring accuracy of surgical cuts using sawblades with different depths of PSI cutting guide slot. Clear operative oncological margins are the main target in malignant bone tumour resections. Novel techniques like patient specific instruments (PSIs) are becoming more popular in orthopaedic oncology surgeries and arthroplasty in general with studies suggesting improved accuracy and reduced operating time using PSIs compared to conventional techniques and computer assisted surgery. Improved accuracy would allow preservation of more natural bone of patients with smaller tumour margin. Novel low-cost technology improving accuracy of surgical cuts, would facilitate highly delicate surgeries such as Joint Preserving Surgery (JPS) that improves quality of life for patients by preserving the tibial plateau and muscle attachments around the knee whilst removing bone tumours with adequate tumour margins. There are no universal guidelines on PSI designs and there are no studies showing how specific design of PSIs would affect accuracy of the surgical cuts. We hypothesised if an increased depth of the cutting slot guide for sawblades on the PSI would improve accuracy of cuts. A pilot drybone experiment was set up, testing 3 different designs of a PSI with changing cutting slot depth, simulating removal of a tumour on the proximal tibia. A handheld 3D scanner (Artec Spider, Luxembourg) was used to scan tibia drybones and Computer Aided Design (CAD) software was used to simulate osteosarcoma position and plan intentioned cuts. PSI were designed accordingly to allow sufficient tumour. The only change for the 3 designs is the cutting slot depth (10mm, 15mm & 20mm). 7 orthopaedic surgeons were recruited to participate and perform JPS on the drybones using each design 2 times. Each fragment was then scanned with the 3D scanner and were then matched onto the reference tibia with customized software to calculate how each cut (inferior-superior-vertical) deviated from plan in millimetres and degrees. In order to tackle PSI placement error, a dedicated 3D-printed mould was used. Comparing actual cuts to planned cuts, changing the height of the cutting slot guide on the designed PSI did not deviate accuracy enough to interfere with a tumour resection margin set to maximum 10mm. We have obtained very accurate cuts with the mean deviations(error) for the 3 different designs were: [10mm slot: 0.76 ± 0.52mm, 2.37 ± 1.26°], [15 mm slot: 0.43 ± 0.40 mm, 1.89 ± 1.04°] and [20 mm: 0.74 ± 0.65 mm, 2.40 ± 1.78°] respectively, with no significant difference between mean error for each design overall, but the inferior cuts deviation in mm did show to be more precise with 15 mm cutting slot (p<0.05). Simulating a cut to resect an osteosarcoma, none of the proposed designs introduced error that would interfere with the tumour margin set. Though 15mm showed increased precision on only one parameter, we concluded that 10mm cutting slot would be sufficient for the accuracy needed for this specific surgical intervention. Future work would include comparing PSI slot depth with position of knee implants after arthroplasty, and how optimisation of other design parameters of PSIs can continue to improve accuracy of orthopaedic surgery and allow increase of bone and joint preservation

Introduction. Patient specific instrumentation (PSI) generates customized guides from an MRI- or CT-based preoperative plan for use in total knee arthroplasty (TKA). PSI software executes the preoperative planning process. Several manufacturers have developed proprietary PSI software for preoperative planning. It is possible that each proprietary software has a unique preoperative planning process, which may lead to variation in preoperative plans among manufactures and thus variation in the overall PSI technology. The purpose of this study was to determine whether different PSI software generate similar preoperative plans when applied to a single implant system and given identical MR images. Methods. In this prospective comparative study, we evaluated PSI preoperative plans generated by Materialise software and Zimmer Patient Specific Instruments software for 37 consecutive knees. All plans utilized the Zimmer Persona™ CR implant system and were approved by a single experienced surgeon blinded to the other software-generated preoperative plan. For each knee, the MRI reconstructions for both software programs were evaluated to qualitatively determine differences in bony landmark identification. The software-generated preoperative plans were assessed to determine differences in preoperative alignment, component sizes, and resection depth. PSI planned bone resection was compared to actual bone resection to assess the accuracy of intraoperative execution. Results. Materialise and Zimmer PSI software displayed differences in identification of bony landmarks in the femur and tibia. Zimmer software determined preoperative alignment to be 0.5° more varus (p=0.008) compared to Materialise software. Discordance in femoral component size prediction occurred in 37.8% of cases (p<0.001) with 11 cases differing by one size and 3 cases differing by two sizes. Tibial component size prediction was 32.4% discordant (p<0.001) with 12 cases differing by 1 size. In cases in which both software planned identical femoral component sizes, Zimmer software planned significantly more bone resection compared to Materialise in the medial posterior femur (1.5 mm, p<0.001) and lateral posterior femur (1.4 mm, p<0.001). Discussion. The present study suggests that there is notable variation in the PSI preoperative planning process of generating a preoperative plan from MR images. We found clinically significant differences with regard to bony landmark identification, component size selection, and predicted bone resection in the posterior femur between preoperative plans generated by two PSI software programs using identical MR images and a single implant system. Surgeons should be prepared to intraoperatively deviate from PSI selected size by 1 size. They should be aware that the inherent magnitude of error for PSI bone resection with regard to both planning and execution is within 2–3 mm. Users of PSI should acknowledge the variation in the preoperative planning process when using PSI software from different manufacturers. Manufacturers should continue to improve three-dimensional MRI reconstruction, bony landmark identification, preoperative alignment assessment, component size selection, and algorithms for bone resection in order to improve PSI preoperative planning process