Musculoskelet Surg DOI 10.1007/s12306-014-0339-7


Patient-specific instrumentation for total knee arthroplasty: a literature review L. Camarda • A. D’Arienzo • S. Morello G. Peri • B. Valentino • M. D’Arienzo

Received: 5 February 2014 / Accepted: 26 September 2014 Ó Istituto Ortopedico Rizzoli 2014

Abstract During the past decade, total knee arthroplasty (TKA) has been markedly increased. Recently, patientspecific custom cutting guides have been commercially introduced in order to achieve an accurate component alignment during TKA. In fact, these cutting blocks are specific to a patient’s knee anatomy and should help the surgeons to perform bone cuts, reducing the complexity of conventional alignment and sizing tools. Nevertheless, there are critical arguments against patient-specific cutting guides for routine use, such as poor evidence and higher costs. Additionally, there are still no mild and long-term results available that describe the clinical outcomes following patient-specific instrumentation of TKR, costeffectiveness and lower revision rates. Aim of the current manuscript was to describe the recent improvements of the surgical technique and instrumentation of TKA, reviewing the recent literature concerning the PSI technology. Keywords Patient-specific instrumentation  TKA  Total knee arthroplasty  PSI

Introduction Total knee arthroplasty (TKA) is considered a successful surgery based on the rate of revision. In fact, implant L. Camarda (&)  A. D’Arienzo  S. Morello  M. D’Arienzo Clinica Ortopedica e Traumatologica, Dipartimento di Discipline Chirurgiche, Oncologiche e Stomatologiche, Universita` degli Studi di Palermo, Via del Vespro, 90100 Palermo, Italy e-mail: [email protected] G. Peri  B. Valentino Dipartimento di Biomedicina Sperimentale e Neuroscienze Cliniche, Universita` degli Studi di Palermo, Palermo, Italy

survival after total knee replacement (TKR) approaches 95 % at 15 years [15, 36]. Further, it has been suggested that the most common cause of TKA revision is an error in surgical technique. TKA survivorship and post-operative performance have been proposed to depend from anatomical and mechanical post-operative alignment [21, 22, 27, 37]. In fact, mechanical alignment exceeding ±3° has been reported to increase the risk of early failure following TKA. The decreased survival due to malalignment is likely due to off-axis loading, polyethylene wear and subsequent implant loosening [23, 29]. Furthermore, it has been reported that a malrotation of the femoral component [5° from the transepicondylar axis alters tibiofemoral kinematics [30] and increases shear forces on the patellar component [2, 30, 39]. For this reason, tibial and femoral components have to be placed as precisely as possible, balancing ligaments in both extension and flexion. However, using conventional surgical techniques, significant errors in post-operative mechanical axis greater than 3° have been reported to occur in at least 10 % of TKAs, including those performed by experienced surgeons [41]. In order to improve the position of implants during TKA, in the last decade computer-assisted navigation (CAS) was introduced in orthopaedic surgery. Over the years, it was observed that CAS allows for a more accurate and reproducible bony resection, ligament balancing, component sizing and kinematics evaluation [1, 7]. Despite the advantage of navigation, several limitations of CAS have been reported such errors on landmark registration, pin loosening and fractures. Further, the increased operative time and risk of deep infection and higher costs of most navigation systems limit its use in low-volume institutions. Even if better alignment may make a difference in the long term, now there are still no proven clinical benefits of CAS in TKA over a conventional technique [16, 17].


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Recently, following an increased technology, threedimensional imaging and custom manufacturing have enabled the development of patient-specific instrumentation (PSI) that are used as cutting jigs. This was done in order to eliminate the negative features of computer navigation, reducing the complexity of conventional alignment and sizing tools, improving operative room efficiency and postoperative alignment. Following this technology, pre-operative radiographs, computer tomography (CT) or magnetic resonance imaging (MRI) are performed on the patient and then used to produce cutting blocks specific to the patient’s knee anatomy. This article will describe the recent improvements of the surgical technique and instrumentation of TKA, reviewing the recent literature of the PSI technology.

Historical perspective and CAS TKA surgery has been one of the most successful orthopaedic procedures during the past two decades. During TKA, bone cuts on the femoral and tibial side are required for the final implantation of respectively the femoral and tibial components. For this reason, alignment guides have been developed to improve the accuracy of femoral and tibial cuts during surgery. Bone cuts in the distal femur are made perpendicular to the mechanical axis, and this is typically made using an intramedullary alignment system. Similarly, the proximal tibia cut is performed perpendicular to the mechanical axis of the tibia using either intramedullary or extramedullary alignment rods. The use of intra- or extramedullary alignment rods has been debated in the past. In fact, both of these systems are susceptible to errors such as improperly positioned entry site and poor centring of the rod within the canal. In order to reduce errors in component alignment during TKA and to improve the accuracy and precision of bone cuts, computer-assisted surgery (CAS) was developed and introduced for orthopaedic surgery. CAS consists of computer platform, tracking system and a rigid body marker. During surgery, after a registration of the anatomical landmarks around the knees and the use of pins placed on the femur and tibia which are attached to the optical reference frames that work as tracking arrays, the system measures the position and orientation of reference frames and it is possible to create a virtual image allowing for intraoperative recording of joint range of motion and kinematics, providing the capability to study the mechanics of knees. Further, it allows enhanced capabilities such as prosthetic sizing and bone resection level. During surgery, CAS helps surgeons to assess each step of TKA, including ligament balancing and kinematic assessments. Several authors have demonstrated that the mechanical axis and the position of components during CAS–TKA are


significantly better than those determined by conventional technique that use intramedullary or extramedullary guides, reducing outliers defined as cases with an alignment [±3° or ±2° in the coronal and sagittal planes [1, 5, 13, 17, 29]. In fact, meta-analysis studies have showed that number of outliers was up to 32 % for the traditional mechanical instrumentation while navigation accomplished values of 9–13 % [17, 29]. However, bony landmark registration to determine resections, implant sizes and rotation is performed by the surgeon manually, and it takes place during the intraoperative portion of the surgical process. Aside from increasing the surgical time, an increased incidence of deep infection due to the longer exposure time could be observed. Further, technical errors inherent to the bony landmark registration process may occur, such as missing the bone due to the overlying soft tissue and cartilage. In fact, small errors in locating these landmarks can lead to significant errors in the orientation of the anatomical reference frames. This could determine errors of components implantation such as malrotation femoral component [45]. The learning curve and high costs of most navigation systems represent another limit of this technology that may limit the widespread of CAS. Furthermore, no long-term result studies or clinical trials provide evidence that navigation helps to reduce the revision rate of TKA.

Patient-specific cutting guides The manufacturing process for TKA implants has improved over the years. Implant designs, sizing options and bearing surface materials have all been improved to enhance the outcomes of TKA. However, the most recent advance in TKA has involved the instrumentation and the processes for TKA implantation with the development of the PSI. This was introduced to help the placing of tibia and femur components in the most accurate way possible, overcoming the limitations of CAS and the disadvantages of additional intraoperative inventory, new skills or surgical time. Furthermore, PSI has been demonstrated to decrease operative time, invasiveness, decreased blood loss and less intraoperative surgeon decision-making [11, 20]. With this technology, a pre-operative MRI or CT is performed on the patient’s knee. Hip and ankle images are also obtained for the evaluation of the overall alignment of the limb. With a specific software program (Mimics, Materialise, Leuven, Belgium), manufacturing engineers turn two-dimensional CT or MRI images into threedimensional representations of the knee and lower limb of the patient’s anatomy. Using these 3D images, the anatomical landmarks of the knee are easily identified. A preoperative plan proposed with bony resections is generated

Musculoskelet Surg Fig. 1 Pre-operative 3D plan with bony resections of femur and tibia

and offered to the operating surgeon. Using a specific software, the surgeon is then able to evaluate the 3D planning of the knee implant with the proposed bony resections. In this phase, the surgeon is able to approve or review the pre-operative plan modifying as necessary bony resection of the tibia and femur. During this phase, it is possible to accurately plan the depth and the coronal orientation of resection, the rotation and the slope of cuts (Fig. 1). After the surgeon’s approval, custom cutting guide that fit on the patient’s native anatomy is manufactured and then sent to the surgeon. Generally, 3 weeks are required to the final production of these cutting guides (Figs. 2, 3). During surgery, the PSI guides are used as slotted cutting guides or for accurate pin position for the use of standard manufacturer resection instrumentation. Custom cutting guide is so used for the primary distal femoral cut and proximal tibial cut. The remaining bone cuts are accomplished with standardized off the shelf instrumentation. If the proposed resection appeared malaligned to surgeon preferences, intraoperative changes could be performed by using standard instrumentation for an additional distal femoral and proximal tibial cut. During surgery, using a PSI–MRI-based attention must be paid to leave cartilage, osteophytes and bone spurs as they work as a referral point for cutting guide stabilization. On the contrary, in case PSI–CT based, the cartilage and soft tissue covering the cutting blocks contact points must be accurately removed with electrocautery in order to totally expose the bone before final jigs fixation. This has to be done because CT is not notable to detect any cartilage and soft tissue. Missing

this surgical step, PSI–CT based could be unstable and consequently inaccurate. Several advantages have been advocated using PSI technology. At first, the surgical time is reduced because many steps of the surgery have been already performed such as pre-operative planning that also help to stream line the surgical technique. Advantage of PSI includes also a decrease in the instrumentation trays optimizing the operative room time. A small reduction of the operating time (from 5 to 12 min) using PSI systems has been found by different authors [8, 33, 34]. This could be helpful for low-

Fig. 2 Distal femur cutting guide. A knee model is also generated to help the surgeon for the intraoperative cutting guide placement


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Finally, a routine use of PSI will considerably increase the cost to the healthcare system because of expensive imaging and additional implant charges to the hospital.


Fig. 3 Proximal tibia cutting guide

volume surgeon who could benefit from PSI by shortening tourniquet times. However, it has been reported that small reductions in operative time alone do not appear to be costeffective for a high-volume subspecialty-trained surgeon [34]. Further, PSI does not require the use of intramedullary rods to determine alignment, and so, there is no violation of the intramedullary canal. Because of the noninvasive system, it has a potential to reduce the incidence of fat embolism and possibly decrease blood loss, post-operative thigh pain and recovery time. This benefit could be comparable to CAS [9, 24], even some authors did not find significant difference in blood loss comparing PSI to conventional TKA [8, 33]. To date, six manufacturers offer PSI technology: Biomet (Warsaw, USA), DuPuy-Synthes (Warsaw, USA), Medacta (Castel San Pietro, Switzerland), Smith & Nephew (Memphis, USA), Wright Medical (Memphis, USA) and Zimmer (Warsaw, USA). Each manufacturers has developed a specific image protocol that requires a specific preoperative MRI or CT scans. Because of different image protocols and manufacturing process of cutting guides, it is still not clear whether this technology is able to obtain what it claims. The MRI-based PSI jigs are thought to be more accurate because it predicts the thickness of the articulate cartilage than the CT-based implants. However, CT-based technique allows to perform a quicker and cheaper exam rather than MRI. Further, bone models generated by MRI scans have been shown to be less accurate than CT-based bone models, because of distorting artefacts that bring to an irregular bone margin [28, 44]. Despite several potential surgical advantages of using PSI technology, there are no long-term implant survival data to support its use. In addition, few studies evaluated the effectiveness of this technology over conventional instrumentation, and results of post-operative alignment accuracy are conflicting.


In the last 3 years, PSI started to be used by orthopaedic surgeons for TKA, even if there was a lack of clinical data supporting benefits of this technology [31]. Furthermore, the peer-reviewed literature on PSI is for the moment still limited, and prospective randomized studies about PSI are few [8, 42]. In addition, even if the philosophical concept of PSI surgical technique is shared by companies and surgeons, methods of planning process, cutting guide productions and final knee implants are different according to the companies. For this reason, controversy still exists concerning the use of this technology on knee surgery. Recently, several authors studied the merits of whether PSI is able to improve the mechanical post-operative alignment. Results between different studies are not clear (Table 1). In addition, mechanical axis evaluation technique is still not completely assessed and literature data are conflicting. Lombardi et al. presented results on 54 TKAs done with PSI using MRI. Radiographic evaluations demonstrated an accurate component position and reconstruction of the mechanical axis. No reoperations, component failures and instability were observed [26]. In 2008, Howell et al. published their initial experience on 48 patients that received an unconstrained TKA (Vanguard, Biomet Inc, Warsaw, Indiana). In this case series, PSI was produced using MRI. Post-operative long-leg CT scan shows an average mechanical axis of -1.4° ± 2.8° valgus [20]. Using the same methods of PSI production, in a case series of 21 patients, Spencer et al. [40] found good limb alignment with a post-operative mechanical axis of 1.2° ± 2.4° varus. Noble et al. performed a prospective randomized study comparing Visionaire PSI (Visionaire; Smith & Nephew, Inc, Memphis) to standard instrumentation. They have shown that patients (n 15) treated using PSI presented a mechanical alignment significantly closer to neutral zero than patients (n 14) treated with standard instrumentation [33]. Similarly, Bali et al. [3] observed that 29 of 32 knees (91 %) operated with the Visionaire PSI system presented a restored mechanical axis within 3° of neutral. Similarly, Vundelinckx et al. [43] reported radiographics and clinical results of 62 patients that underwent a TKA from 2010 to 2011. Patients were randomized to make a study group of 31 Visionaire PSI patients and an equal control group of 31. Clinical evaluations and post-operative full leg X-rays did not show differences between PSI and conventional techniques for satisfaction, clinical and radiological outcomes. However, in the Visionaire group, 13 out of 31

291 25




Ensini et al. [14]

Barrett et al. [4]

Chotanaphuti et al. [12]


Ng et al. [32]

Koch et al. [25] Ensini et al. [14]


Boonen et al. [6]

25 (30 TKR)


Chareancholvanich et al. [8]



Lustig et al. [28]

Scholes et al. [38]


Vundelinckx et al. [43]

Chen et al. [10]



Spencer et al. [40]



Howell et al. [20]

Noble et al. [33]

51 (54 TKR)

Lombardi et al. [26]

Bali et al. [3]

Number of patients (PSI)


Table 1 PSI studies

RCT (PSI vs conventional)

Case series, multicenter, nonrandomized trial (PSI vs conventional)

RCT CT-based versus MRI-based

Case series RCT CT-based versus MRI-based

Case series

Case series

Case series (PSI vs conventional)

RCT (PSI vs conventional)

RCT (PSI vs conventional)

Case series

RCT (PSI vs conventional)

Case series

RCT (PSI vs conventional)

Case series

Case series

Case series

Study type

CT-based TruMatch (DePuy Synthes)

CT-based TruMatch (DePuy Synthes)

MRI-based Visionaire (Smith & Nephew)

CT-based MyKnee (Medacta) CT-based MyKnee (Medacta)

MRI-based PSI (Nexgen, Zimmer)

MRI-based PSI (Zimmer)

MRI-based Signature System (Vanguard, Biomet)

MRI-based Signature System (Vanguard, Biomet)

MRI-based PSI (NexGen–Zimmer)

MRI-based Visionaire (Smith & Nephew)

MRI-based Visionaire (Smith & Nephew)

MRI-based Visionaire (Smith & Nephew)

MRI-based Visionaire (Smith & Nephew)

MRI-based OtisMed Inc (Triathlon, Stryker)

MRI-based OtisMed Inc (Vanguard, Biomet)

MRI-based (Vanguard, Biomet)

Patient-specific instrumentation

-0.5° ± 1.5°

2.23° ± 1.9°

1.7° ± 1.7°

Mean HKA of 180.1 (±2.0 DS) 2.5° ± 2.3°

Mean HKA of 179.2 (±3.4 DS)

-0.5 ± 2.8 (range -6.5/5.0)

Mean HKA of 180.6°

Mean HKA of 179° (±2.8 DS)

Mean HKA of 179° (176°–183°)

Not reported

Not reported

0.1° varus ± 2.0° (range 4° varus–5° valgus)

1.7° (range 0°–6°)

1.2° varus ± 2.4° (range 4° varus–6° valgus)

-1.4° ± 2.8°

Alignment of 4°–8° valgus in all cases (n 44)

Mechanical axis

5 % [±3°

19 % [±3°

18 % [± 3° on all three anatomical planes

12.4 % [±3° mechanical axis 37 % [±3° on all three anatomical planes

9 % [±3° of coronal alignment

27 % [±3°

9 % [±3° mechanical axis

30 % [±3° mechanical axis

2.5 % [±3° tibio-femoral alignment

45.5 % sagittal

20.7 % coronal

Not reported

10 %

Not reported

14 % [3° (mechanical axis)

Not reported

Not reported

% of outliers

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patients (43 %) did not reach full extension, in contrast to 6 out of 31 patients (19 %) in the control group. Authors tried to explain this issue with a tighter placement of the prosthesis in the Visionaire group [43]. Recently, Lustig et al. reported results of consecutive series of 60 patients treated with Visionaire PSI. Intraoperative computer navigation was used by authors to evaluate the accuracy of the cutting blocks. They observed that 79.3 % of the sample was within ±3° of the pre-operative plan. However, the rotational and sagittal alignment presented an unsatisfactory accuracy with, respectively, 77.2 and 54.5 % results within ±3° [28]. Furthermore, authors affirmed that the variation between the planned sagittal alignment and the operative measurements could be secondary to an error of image acquisition and interpretation of the 3D image using MRIs [28]. Recently, Boonen et al. [6] and Chareancholvanich et al. [8] published the results of their RCT studies comparing PSI (PSI Zimmer Inc., Warsaw, USA and Signature System, Vanguard, Biomet, Inc., Warsaw) versus conventional instrumentation. Both authors came to the same conclusion that there were no significant differences between the groups in terms of tibiofemoral angle or femoral component alignment. Also, Ng et al. [32] studied the accuracy of the signature system. Otherwise, they found the overall mechanical axis that passed through the central third of the knee was more frequent with PSI System (88 %) than with conventional instrumentation (78 %). Moreover, the overall mean hip–knee–ankle angle for PSI system was similar to conventional instrumentation (180.6 vs. 181.1, respectively), and fewer hip–knee–ankle angle outliers (±3) were observed using PSI (9 %) than conventional instrumentation (22 %). Finally, Scholes et al. [38] evaluated 25 patients that underwent 30 primary TKAs using an MRIbased PSI system (PSI Zimmer Inc., Warsaw, USA). They found a percentage of outliers ([3°) of 27 %. Further, it was observed that in that case series, Zimmer PSI does not recreate the pre-operative plan in terms of alignment and bone cut depth. These results are comparable to that described by Chen et al. [10] who found a percentage of outliers of 31 % using the same MRI-based PSI system (PSI Zimmer Inc., Warsaw, USA). As PSI–MRI-based systems, to date a not very extensive literature is available concerning PSI–CT-based systems. To our knowledge, just four manuscripts addressed the use of CT scan analysis for the pre-operative planning process and cutting guide productions. Koch et al. [25] reported the radiological outcome of 291 TKA using a CT-based patient-specific cutting block technique (MyKnee, Medacta International S.A., Castel San Pietro, Switzerland). Using post-operative long-standing X-ray, they found post-operative average hip–knee–ankle angle (HKA) of 180.1° ± 2.0°. Furthermore, in their cohort, a lower


number of outliers for the frontal mechanical axis were found (36 cases, 12.4 %). These results were reported to be clearly better than those achieved and published with conventional instrumentation, comparable to that obtained with navigation [11, 29]. Both intraoperative and post-operative final component alignments were assessed by Ensini et al. [14] who compared the accuracy of two different PSI systems for TKR, one CT based (Myknee, Medacta) and one MRI/X-ray based (Visionaire, Smith and Nephew). They found that for both PSI systems, the mean final alignments were found to be satisfactory in all three anatomical planes. Outliers coronal planes were found to be smaller than 17 %, inferior to those established for conventional TKR, i.e. 18–32 % [17, 29]. Barrett et al. [4] compared results of patients treated with conventional instrumentation, CAS and PSI– CT-based TruMatch personalized solutions (DePuy Synthes, Warsaw, IN). In this study, the percentage of outliers was of 23 % in the conventional group, 19 % in the PSI group and 18 % in the CAS group. Recently, Chotanaphuti et al. [12] reported the results of their RCT study comparing PSI (CT-based TruMatch) versus conventional instrumentation. They observed no differences in the accurate post-operative mechanical axis between the custom cutting blocks group and conventional TKA group. However, they found a better accuracy in rotational alignment in the PSI group. As coronal alignment and mechanical axis result, there is a contradictory between studies regarding the improvement of sagittal and rotational accuracy of PSI over conventional instrumentation for TKA [18, 28, 35]. However, femoral rotation seems to be more accurate using PSI technology than conventional instrumentation [12, 18, 35]. Nevertheless, there is a lack of consensus regarding the capacity for post-operative radiographs, computer navigation, twodimensional CT or three-dimensional CT to assess components alignment in post-operative knees [19]. Notwithstanding, CT scans to our knowledge can be considered the best methods to evaluate the rotation of the implants [35].

Conclusion Despite the availability of few peer-reviewed papers, PSI in knee arthroplasty was able to attract surgeons attention as an alternative to traditional instrumentation and computer navigation. However, the effectiveness of this technology over conventional instrumentation is not completely clear, and recent data are conflicting. More work needs to be done to more clearly define the place of PSI in TKA for low- and high-volume surgeons, and to evaluate clinically important improvements in outcomes or patient satisfaction, patient-specific cutting blocks are used for TKA.

Musculoskelet Surg Conflict of interest of interest.

The authors declare that they have no conflict 15.

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Patient-specific instrumentation for total knee arthroplasty: a literature review.

During the past decade, total knee arthroplasty (TKA) has been markedly increased. Recently, patient-specific custom cutting guides have been commerci...
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