Three-dimensional (3D) printing has numerous applications and has gained much interest in the medical world. The constantly improving quality of 3D-printing applications has contributed to their increased use on patients. This paper summarizes the literature on surgical 3D-printing applications used on patients, with a focus on reported clinical and economic outcomes. Three major literature databases were screened for case series (more than three cases described in the same study) and trials of surgical applications of 3D printing in humans. 227 surgical papers were analyzed and summarized using an evidence table. The papers described the use of 3D printing for surgical guides, anatomical models, and custom implants. 3D printing is used in multiple surgical domains, such as orthopedics, maxillofacial surgery, cranial surgery, and spinal surgery. In general, the advantages of 3D-printed parts are said to include reduced surgical time, improved medical outcome, and decreased radiation exposure. The costs of printing and additional scans generally increase the overall cost of the procedure. 3D printing is well integrated in surgical practice and research. Applications vary from anatomical models mainly intended for surgical planning to surgical guides and implants. Our research suggests that there are several advantages to 3D-printed applications, but that further research is needed to determine whether the increased intervention costs can be balanced with the observable advantages of this new technology. There is a need for a formal cost–effectiveness analysis.

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3D-printing techniques in a medical setting: a systematic literature review

Osteoarthritis is the most common joint disease and a major cause of disability. Distinct biological processes are considered crucial for the development of osteoarthritis and are assumed to act in concert with additional risk factors to induce expression of the disease. In the classical weightbearing joints, one such risk factor is an unfavourable biomechanical environment about the joint. While the elbow has long been considered a non-weightbearing joint, it is now assumed that the tissues of the upper extremity may be stressed to similar levels as those of the lower limb, and that forces across the elbow are in fact very high when the joint is extended from a flexed position. This review examined the available basic science, preclinical and clinical evidence regarding the role of several unfavourable biomechanical conditions about the elbow on the development of osteoarthritis: post-traumatic changes, osteochondritis dissecans, instability or laxity and malalignment. Post-traumatic osteoarthritis following fractures is well recognized, however, the role of overload or repetitive microtrauma as risk factors for post-traumatic osteoarthritis is unclear. The natural course of untreated cartilage defects in general, and osteochondritis dissecans at the elbow in particular, remains incompletely understood to date. However, larger lesions and older age seem to be associated with more symptoms and radiographic changes in the long term. Instability seems to play a role, although the association between instability and osteoarthritis is not yet clearly defined. No data are available on the association of malalignment and osteoarthritis, but based on force estimations across the elbow joint, it seems reasonable to assume an association.

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Biomechanical Considerations in the Pathogenesis of Osteoarthritis of the Knee

Background: Coronal malalignment occurs frequently in total knee arthroplasty (TKA) and reduces implant longevity and function. Designed to improve consistency and efficiency, patient- specific positioning guides (PSPG) generated from preoperative imaging studies represent a paradigm shift from manual instrumentation (MI) and intraoperative computer navigation. Purposes: We compare the efficacy of PSPG to MI in (1) restoring mechanical axis of the extremity and (2) achieving neutral alignment of the femoral and tibial components. Methods: We retrospectively examined 696 postoperative anteroposterior standing long-leg radiographs after TKA (545 PSPG, 151 MI) by two surgeons. Coronal alignment was assessed by determining the zone in which the overall mechanical axis (OMA) passed through the knee, measuring the hip-knee-ankle (HKA) angle between the tibial and femoral mechanical axes, and finally, noting the alignment of the femoral and tibial components with respect to their mechanical axes. Results: The OMA passed through the central third more frequently with PSPG than MI for both surgeons (JHD: 86.6% vs. 77%, p = 0.02; AVL: 86.4% vs. 74.5%, p = 0.11). For the senior author, while percent of HKA outliers >3i,° was similar between PSPG and MI, the mean error from neutral for these patients was significantly less with PSPG than MI (4.50i,° vs. 5.25i,°, p = 0.0031). The tibial component demonstrated no significant difference between PSPG and MI. With PSPG, average individual deviation from neutral for the femoral component was significantly less (0.91i,° vs. 1.34i,°, p = 0.0005) and had fewer outliers >2i,° (4.9% vs. 19.6%, p = 0.017). Discussion: Improved coronal alignment in total knee arthroplasty (TKA) is associated with greater patient satisfaction, better functional scores and increased implant longevity [11,30,31,36]. Recently, preoperative three-dimensional imaging and custom manufacturing have enabled the development of patient-specific positioning guides (PSPG). Designed to improve consistency and efficiency, PSPG represents a paradigm shift away from intramedullary and extramedullary guides, or manual instrumentation (MI), and an evolution from intraoperative computer-assisted navigation (CAN). Even in the hands of experienced surgeons, MI frequently results in significant component angulation and mechanical axis malalignment [32]. Multiple studies support the restoration of a neutral axis as a critical factor in implant performance and potential longevity of total knee arthroplasty [2, 3, 5, 18, 41, 44]. Intraoperative CAN has been shown to improve precision and accuracy of alignment compared to MI with a reduction in the number of outliers (less than 3i,° varus/valgus) [32, 38] and the amount of blood loss [39], but is hindered by time-consuming landmark registration, increased operative length [7], greater cost, the risk for stress fracture, pin loosening, and a substantial learning curve [6, 22, 29, 43]. Patient-specific positioning guides, on the other hand, purportedly eliminate many of the disadvantages of CAN while still allowing the bone resections to match the measured overall mechanical axis. While accurate and precise alignment guides are potent tools in restoring the proper overall mechanical axis, they are not a substitute for careful preoperative planning, good clinical and intraoperative judgment, appropriate soft tissue balancing, and precise implantation technique. Nevertheless, patient-specific positioning guides can provide the first step in the right direction to a successful TKA. Conclusions: Patient-specific positioning guides can assist in restoration of the mechanical axis with reduction in outliers. Level of Evidence: Level III, retrospective case-control study

Improved Accuracy of Alignment With Patient-Specific Positioning Guides Compared with Manual Instrumentation in TKA

Successful total knee arthroplasty (TKA) is dependent on the correct alignment of implanted prostheses. Major clinical problems can be related to poor femoral component positioning, including sagittal plane and rotational malalignment. A prospective randomized study was designed to test whether an optical navigation system for TKA achieved greater implantation precision than a non navigated technique. The primary variable was rotation of the femoral component in the transverse plane measured from post operative radiographs and CT images. Sixty-four patients were included in the study. All patients received the Duracon total knee prosthesis. The patients were randomly divided into two groups; Group C patients underwent conventional TKR without navigation, Group N patients underwent TKR using a computer assisted Knee Navigation System. Analysis revealed that patients in Group N had significantly better rotational alignment and flexion angle of the femoral component than patients in Group C. In addition, superior post operative alignment of the mechanical axis, posterior tibial slope, and rotational alignment was achieved for patients in Group N. The use of a navigation system provides improved alignment accuracy. Specifically, it can help to avoid femoral malrotation and errors in axial alignment.

Navigation improves accuracy of rotational alignment in total knee arthroplasty

Background
Total knee replacement (TKR) is a common and often painful operation. Femoral nerve block (FNB) is frequently used for postoperative analgesia.

Objectives
To evaluate the benefits and risks of FNB used as a postoperative analgesic technique relative to other analgesic techniques among adults undergoing TKR.

Search methods
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) 2013, Issue 1, MEDLINE, EMBASE, CINAHL, Web of Science, dissertation abstracts and reference lists of included studies. The date of the last search was 31 January 2013.

Selection criteria
We included randomized controlled trials (RCTs) comparing FNB with no FNB (intravenous patient-controlled analgesia (PCA) opioid, epidural analgesia, local infiltration analgesia, and oral analgesia) in adults after TKR. We also included RCTs that compared continuous versus single-shot FNB.

Data collection and analysis
Two review authors independently performed study selection and data extraction. We undertook meta-analysis (random-effects model) and used relative risk ratios (RRs) for dichotomous outcomes and mean differences (MDs) or standardized mean differences (SMDs) for continuous outcomes. We interpreted SMDs according to rule of thumb where 0.2 or smaller represents a small effect, 0.5 a moderate effect and 0.8 or larger, a large effect.

Main results
We included 45 eligible RCTs (2710 participants) from 47 publications; 20 RCTs had more than two allocation groups. A total of 29 RCTs compared FNB (with or without concurrent treatments including PCA opioid) versus PCA opioid, 10 RCTs compared FNB versus epidural, five RCTs compared FNB versus local infiltration analgesia, one RCT compared FNB versus oral analgesia and four RCTs compared continuous versus single-shot FNB. Most included RCTs were rated as low or unclear risk of bias for the aspects rated in the risk of bias assessment tool, except for the aspect of blinding. We rated 14 (31%) RCTs at high risk for both participant and assessor blinding and rated eight (18%) RCTs at high risk for one blinding aspect.

Pain at rest and pain on movement were less for FNB (of any type) with or without a concurrent PCA opioid compared with PCA opioid alone during the first 72 hours post operation. Pooled results demonstrated a moderate effect of FNB for pain at rest at 24 hours (19 RCTs, 1066 participants, SMD -0.72, 95% CI -0.93 to -0.51, moderate-quality evidence) and a moderate to large effect for pain on movement at 24 hours (17 RCTs, 1017 participants, SMD -0.94, 95% CI -1.32 to -0.55, moderate-quality evidence). Pain was also less in each FNB subgroup: single-shot FNB, continuous FNB and continuous FNB + sciatic block, compared with PCA. FNB also was associated with lower opioid consumption (IV morphine equivalent) at 24 hours (20 RCTs, 1156 participants, MD -14.74 mg, 95% CI -18.68 to -10.81 mg, high-quality evidence) and at 48 hours (MD -14.53 mg, 95% CI -20.03 to -9.02 mg), lower risk of nausea and/or vomiting (RR 0.47, 95% CI 0.33 to 0.68, number needed to treat for an additional harmful outcome (NNTH) four, high-quality evidence), greater knee flexion (11 RCTs, 596 participants, MD 6.48 degrees, 95% CI 4.27 to 8.69 degrees, moderate-quality evidence) and greater patient satisfaction (four RCTs, 180 participants, SMD 1.06, 95% CI 0.74 to 1.38, low-quality evidence) compared with PCA.

We could not demonstrate a difference in pain between FNB (any type) and epidural analgesia in the first 72 hours post operation, including pain at 24 hours at rest (six RCTs, 328 participants, SMD -0.05, 95% CI -0.43 to 0.32, moderate-quality evidence) and on movement (six RCTs, 317 participants, SMD 0.01, 95% CI -0.21 to 0.24, high-quality evidence). No difference was noted at 24 hours for opioid consumption (five RCTs, 341 participants, MD -4.35 mg, 95% CI -9.95 to 1.26 mg, high-quality evidence) or knee flexion (six RCTs, 328 participants, MD -1.65, 95% CI -5.14 to 1.84, high-quality evidence). However, FNB demonstrated lower risk of nausea/vomiting (four RCTs, 183 participants, RR 0.63, 95% CI 0.41 to 0.97, NNTH 8, moderate-quality evidence) and higher patient satisfaction (two RCTs, 120 participants, SMD 0.60, 95% CI 0.23 to 0.97, low-quality evidence), compared with epidural analgesia.

Pooled results of four studies (216 participants) comparing FNB with local infiltration analgesia detected no difference in analgesic effects between the groups at 24 hours for pain at rest (SMD 0.06, 95% CI -0.61 to 0.72, moderate-quality evidence) or pain on movement (SMD 0.38, 95% CI -0.10 to 0.86, low-quality evidence). Only one included RCT compared FNB with oral analgesia. We considered this evidence insufficient to allow judgement of the effects of FNB compared with oral analgesia.

Continuous FNB provided less pain compared with single-shot FNB (four RCTs, 272 participants) at 24 hours at rest (SMD -0.62, 95% CI -1.17 to -0.07, moderate-quality evidence) and on movement (SMD -0.42, 95% CI -0.67 to -0.17, high-quality evidence). Continuous FNB also demonstrated lower opioid consumption compared with single-shot FNB at 24 hours (three RCTs, 236 participants, MD -13.81 mg, 95% CI -23.27 to -4.35 mg, moderate-quality evidence).

Generally, the meta-analyses demonstrated considerable statistical heterogeneity, with type of FNB, allocation concealment and blinding of participants, personnel and outcome assessors reducing heterogeneity in the analyses. Available evidence was insufficient to allow determination of the comparative safety of the various analgesic techniques. Few RCTs reported on serious adverse effects such as neurological injury, postoperative falls or thrombotic events.

Authors' conclusions
Following TKR, FNB (with or without concurrent treatments including PCA opioid) provided more effective analgesia than PCA opioid alone, similar analgesia to epidural analgesia and less nausea/vomiting compared with PCA alone or epidural analgesia. The review also found that continuous FNB provided better analgesia compared with single-shot FNB. RCTs were insufficient to allow definitive conclusions on the comparison between FNB and local infiltration analgesia or oral analgesia.

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Femoral nerve blocks for acute postoperative pain after knee replacement surgery

This investigation evaluated the Smith and Nephew VISIONAIRE patient-specific cutting block (PSCB) system for total knee arthroplasty. A consecutive series of 60 patients was recruited. Intraoperative computer navigation was used to evaluate the accuracy of the cutting blocks in the coronal and sagittal planes for the tibia, as well as rotational plane for the femur. The PSCB would have placed 79.3% of the sample within ±3° of the preoperative plan in the coronal plane, while the rotational and sagittal alignment results within ±3° were 77.2% and 54.5% respectively. The VISIONAIRE PSCB system achieved unacceptable accuracy when assessed by computer navigation. There might be many sources of error, but caution is recommended before using this system routinely without objective verification of alignment.

Unsatisfactory Accuracy as Determined by Computer Navigation of VISIONAIRE Patient-Specific Instrumentation for Total Knee Arthroplasty

Background: High tibial osteotomy (HTO) is a method used to treat medial compartmental osteoarthritis in the knee. The realignment of the knee changes the loading patterns within the joint and may allow for regeneration of articular cartilage. Magnetic resonance imaging methods can be used to assess the quality of the regenerated cartilage.Hypothesis: Altering mechanical alignment through HTO will have predictable effects on articular cartilage, allowing cartilage preservation and possible regeneration. Quality of regenerated cartilage will be inferior to normal articular cartilage.Study Design: Case series; Level of evidence, 4.Methods: Ten patients undergoing medial opening wedge HTO were evaluated using dGEMRIC methods (ie, delayed gadolinium-enhanced magnetic resonance imaging of cartilage) preoperatively and at 6 months, 1 year, and 2 years after HTO. Magnetic resonance images were evaluated by hand segmentation, and T1Gd relaxation times reflective of glycosaminoglycan content were determined for th...

Articular Cartilage Changes in Patients With Osteoarthritis After Osteotomy

In contrast to radiographic measurements, MRI provides multiple slices of the knee joint in the sagittal plane, making it possible to assess the medial and lateral tibial slope separately. The purpose of this study is to investigate the effect of medial open-wedge high tibial osteotomy (MOWHTO) on bony and meniscal slope in the medial and lateral tibiofemoral compartments. It was hypothesised that greater changes on the medial tibial plateau would be observed compared with the lateral one. A retrospective analysis of prospectively collected data was performed on pre- and post-operative MRIs from 21 patients (17 men and 4 women; age 52 ± 9 years). Inclusion criteria were varus alignment, medial compartment osteoarthritis and election for a primary MOWHTO. Each patient had a preoperative and a post-operative high-resolution MRI (3Tesla, Magnetom Trio, Siemens AG) at an average follow-up of 2.1 years. A previously published method was used to measure bony and meniscal slope for each compartment. The difference between pre- and post-operative tibial slope for both compartments was calculated and associated with the amount of frontal correction. There was a significant increase in bony tibial slope in both compartments following MOWHTO. When a change in bony tibial slope was detected in an individual patient, the change was larger in the medial compartment, with the average change also significantly greater (p < 0.01) in the medial compartment (2.4° ± 1.3°) compared with the lateral compartment (0.9° ± 1.1°). There was also a significant increase (p < 0.01) in the lateral tibial meniscal slope of 0.9° ± 1.4°, which was equivalent to the change in the bony lateral slope. The amount of frontal correction was not significantly associated with the amount of change in slope. The results suggest that the modification of the bony slope is larger in the medial compartment after MOWHTO, which is likely related to the location of the hinge on the lateral tibial cortex. These findings suggest that consideration of the medial and lateral tibial slope intra-operatively could be important to identify the optimal location of the hinge. However, further studies are required before recommending any modification to the surgical technique, as the potential clinical consequences of tibial slope alterations remain unknown. IV.

Different changes in slope between the medial and lateral tibial plateau after open-wedge high tibial osteotomy

The introduction of patient-specific instruments (PSI) for guiding bone cuts could increase the incidence of malalignment in primary total knee arthroplasty. The purpose of this study was to assess the agreement between one type of patient-specific instrumentation (Zimmer PSI) and the pre-operative plan with respect to bone cuts and component alignment during TKR using imageless computer navigation. A consecutive series of 30 femoral and tibial guides were assessed in-theatre by the same surgeon using computer navigation. Following surgical exposure, the PSI cutting guides were placed on the joint surface and alignment assessed using the navigation tracker. The difference between in-theatre data and the pre-operative plan was recorded and analysed. The error between in-theatre measurements and pre-operative plan for the femoral and tibial components exceeded 3° for 3 and 17 % of the sample, respectively, while the error for total coronal alignment exceeded 3° for 27 % of the sample. The present results indicate that alignment with Zimmer PSI cutting blocks, assessed by imageless navigation, does not match the pre-operative plan in a proportion of cases. To prevent unnecessary increases in the incidence of malalignment in primary TKR, it is recommended that these devices should not be used without objective verification of alignment, either in real-time or with post-operative imaging. Further work is required to identify the source of discrepancies and validate these devices prior to routine use. II.

Patient-specific instrumentation for total knee arthroplasty does not match the pre-operative plan as assessed by intra-operative computer-assisted navigation

Background: While single shot femoral nerve blocks and indwelling femoral nerve catheters provide significant peri-operative analgesia, there are small but serious risks of neurovascular complications. We aimed to determine the incidence and characterise the nature of neural complications arising from femoral nerve blocks performed for knee surgery. Methods: One thousand eight hundred and two patients receiving a femoral nerve block for knee surgery during the study period were screened. Patients with possible neurological symptoms were evaluated with a detailed physical examination and self-report questionnaires. Also measures of depression, anxiety and tension/stress were collected. Results: In the patients screened, an incidence of 1.94% was found. Of the 24 patients available for testing, 4 had bilateral symptoms following bilateral nerve blocks. All had sensory abnormalities in the distribution of the femoral nerve. The incidence was significantly higher in females (females = 2.5%, males = 0.83% p = 0.01) and in patients receiving a single shot block (single shot = 2.66%, femoral catheter = 0.93, p = 0.01). Conclusions: The incidence of neurological complication after FNB was higher in this series than typically reported and the symptoms significantly influenced the quality of life in the affected cases. The decision to include a femoral nerve block in the peri-operative analgesic regimen should be made on an individual basis considering the risks and benefits. Level of evidence Therapeutic level IV.

Corey Scholes

Papers

Unsatisfactory Accuracy as Determined by Computer Navigation of VISIONAIRE Patient-Specific Instrumentation for Total Knee Arthroplasty

Articular Cartilage Changes in Patients With Osteoarthritis After Osteotomy

Different changes in slope between the medial and lateral tibial plateau after open-wedge high tibial osteotomy

Patient-specific instrumentation for total knee arthroplasty does not match the pre-operative plan as assessed by intra-operative computer-assisted navigation

Incidence and severity of complications due to femoral nerve blocks performed for knee surgery