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Title: Patient Specific Instrumentation versus Manual Instrumentation In Total Knee Arthroplasty; A Comparison Study

Author(s): Samih Tarabichi MD1, Usame Hassan Saleh MD1, Ali Sina Shahi MD2*

Affiliattion(s): 1-Tarabichi Joint Replacement Institute
2-Postdoctrate Research Fellow, Rothman Institute

* Corresponding Author

Vol 1, Num 1, July 2014




Introduction: Variety of techniques has been introduced to improve the outcomes of total knee arthroplasty (TKA). Choosing the best technique has always been a challenge for Orthopaedic surgeons, as each technique has its own advantages and disadvantages. The aim of this study is to compare the efficacy of patient specific guides with manual instrumentations regard with, retaining the neutral alignments.

Materials and Methods: Patients have been allocated into two groups. Each group has been operated with different technique, one using the patient-specific guides (PSG) and the other group with the manual instrumentations (MI). Coronal and sagittal alignments have been evaluated in all the patients. A comparison in duration of the surgery and tourniquet time were also been performed.

Results: 289 knees were evaluated, 250 operated with MIs and 29 knees with PSGs. The duration of the surgery and tourniquet time were significantly longer using manual instrumentations. The results regarding retaining the neutral alignments in coronal and sagittal planes had no difference.

Conclusion: The efficacy of TKA in retaining the neutral alignment in sagittal and coronal plane has no significant difference using either technique in hands of an experienced surgeon. But the surgery and tourniquet times have significantly decreased using PSGs.




The main purpose of total knee arthroplasty (TKA) is recovering the neutral overall mechanical axis. It has been presented by numerous biomechanical (1) and clinical studies.(2-5) They have all shown, with coronal and sagittal malalignment, higher failure rates, more strain, and lower functional scores are observed. It can also lead to early loosening and increased polyethylene wear.(6-8) Varus or valgus malalignment has been known as the most common cause of early loosening, so restoring the mechanical axis is correlated with implant survival. Some studies have shown more rapid failure and less satisfactory functional resource are associated with alignment errors of more than 3 degrees. (9,10) New technologies like three-dimensional imaging and custom manufacturing have attributed to the new techniques for TKA, patient-specific instrumentations (PSI). The aim of this system is mainly to improve alignment accuracy and precision, while minimizing the size and number of required instruments, and also reducing the duration of the surgery. PSI technology uses pre-operative MRI to design individualized jigs. Despite manual instrumentations (MI) with intra-medullary and extra-medullary alignment rods which uses ordinary jigs, the individualize jigs sits on the articular surface of the proximal tibia and distal femur to facilitate pin placement. (Fig. 1) Some other technologies also have been introduced to improve the alignments like computer-assisted navigation. But this technology is not very popular, due to the increase of the surgical time (25-27), difficulty with landmark registration (28-29), associated cost (30,31) and pin loosening. (32,33) The aim of this study was to compare the PSI system with the conventional MI system, to define whether it could improve the results of achieving the neutral alignment in lower extremity. A comparison regarding the duration of the surgery and tourniquet time has also been made.

    Figure 1: Custom instruments are used to determine the exact location of the pins.

    Materials and Methods

    From February 2010 to December 2012, one of the author (ST) performed primary TKA in 15 patients (29 knees) using PSIs (Zimmer Inc. USA) and 476 patients (852 knees) using MI (manual instrument) (extra-medullary tibial and intramedullary femoral jigs). All patients whom were disabled by knee arthritis, had acceptable medical risk, and failed non-operative treatment were considered as candidates for TKA. These patients were allocated into two groups: PSI and MI. The inclusion criteria for PSI group were: 1) the ability and inclination to undergo preoperative MRI, 2) the patience to wait 3 to 4 weeks for the surgery (this duration was needed for instruments to be provided), and 3) the proclivity to the relatively new technology regarding higher cost. Exclusion criteria were: 1) Patients with a metallic hardware within 10 cm of their knee or revision cases, as it interferes with the MRI. 2) Patients with pacemaker or any other condition that cause prohibition to have MRI, were also been excluded. 250 patients, whom underwent TKA with the manual instrumentations and had adequate radiographs (including post-operative weight bearing alignment view), were retrospectively reviewed and allocated to the MI group; the exclusion criteria were lower limb fractures or periprosthetic fractures after TKA. PSI system was used according to the manufacturer's instructions. First a preoperative MRI was performed. The MRI machines required for this study must have magnet strength of at least a 1.5 T (Tesla) and also as the imaging device it should has standard knee coil, to be compatible with the imaging protocol. The pre-operative study was sent to the manufacturer company (Zimmer, Inc. USA). The data was uploaded on the software planner of the company. Then the templates and alignment of the components were reviewed, by the surgeon. And the final plan was approved.

    Surgical techniques

    All patients were informed about current treatment options including different surgical techniques. Moreover, a written instruction of the entire study protocol, regarding details of the study participation was given to all the patients. Each group has been operated by the same surgeon in the same hospital. For all the included patients Nexgen LPS-flex fixed bearing knee prosthesis (Zimmer Inc., USA) was used.

    The MI Group:

    To reduce blood in the field of surgery, a pneumatic tourniquet at a pressure of 350 mmHg was used after exsanguination. By having a mid-line skin incision of 10-14 cm, sub-vastus approach was performed on all the patients. After exposure of the knee the rest of the surgery was carried out using intra-medullary femoral and extra-medullary tibial instruments.

    The PSI Group:

    In these patients, following exposure of the knee using sub-vastus approach, the PSI jigs were carefully positioned over the articular surfaces, and accurate fit was confirmed, starting by femur. Then, drill holes and pins were placed in the peri-articular bone, guided by the PSI jig. These marks were used to determine the orientation of standard cutting blocks. The rest of the TKA procedure was continued as routine.

    Radiographic Measurements

    All patients had complete radiographic follow-up examinations. Radiographies consist of full-length alignment antero-posterior view and lateral knee view, with the patient lying and the knee in 30 degrees of flexion. Two independent reviewers blinded to the surgical technique evaluated these radiographies using digital tools. Mechanical axis, tibial and femoral coronal angle were evaluated using the alignment views. (Fig. 2)

    The positions of the components, tibial and femoral sagittal angles were assessed using the lateral views. (Fig. 3) The site of radiolucent lines at the cement-bone junction was determined as recommended by the Knee Society. [12] Duration of the surgery and tourniquet time were also compared in these groups. The moment of skin incision to the last suture of the skin closure defined the surgical duration. And tourniquet time was determined from the moment it reached to pressure of 350 mmHg till the start of deflation.

    Statistical methods

    The Chi-square test was used to compare two qualitative variables. When the variables were quantitative, first the assumption of normality was determined using the Kolmogorov–Smirnov test, then Student t-test was used, where P<0.05 was considered statistically significant. The data were analyzed with the SPSS statistics pack, version 20 for Mac.

    Figure 2: Alignment view showing the overall mechanical axis in the coronal plane. The femoral and tibial angles were measured by the intersection of a line drawn tangent to the base of each component and the mechanical axis. a = coronal femoral angle, and b = coronal tibial angle.
    Figure 3: Lateral knee radiographs were used to determine the femoral sagittal angle (femoral flexion) (A) and tibial sagittal angle (tibial posterior slope). (B)


    Results We retrospectively reviewed 168 patients whom underwent primary TKA. Of these patients, 250 knees were operated using manual instrumentations, and allocated to the MI group. 29 TKA were performed using patient specific instrumentations, which allocated to the PSI group. There were 4 males and 16 females in the PSI group; the mean age was 62±8 years. And among the MI group there were 53 males and 99 females with the mean age of 59±7 years. The demographic data are presented in table 1. The mean duration of the surgery and tourniquet time were found to be significantly longer using manual instrumentations. (P< 0.001)(Table 2.) In regard with the knee alignment and the position of the femoral and tibial components in coronal and sagittal planes, radiographic findings were similar and had no significant difference in both groups. Assuming 3° as the tolerance level for outliers, their prevalence ranged from 6.8% to 13.7% for all the measures in the PSI group and from 12.0% to 20.8% in the MI group. These differences were not statistically significant. (P>0.05) Also, patients had no major clinical difference. (Table 3.) There was no severe complication, except in two patients (1.3%) among the MI group whom had anterior femoral notching. One knee in the PSI group developed a wound infection, which then debridement was performed and intra-venous anti-biotic was applied for 6 weeks.

    Table 1: Demographics
    Table 2: Duration comparison of the two techniques
    Table 3: Radiographic measures


    Discussion Several techniques and approaches have been presented to perform TKA. Each has its own advantages and disadvantages. There are many articles supporting, implant longevity will increase as the neutral axis is restored. (1,2,4,5,13,14) There is also interest in the effect of coronal and sagittal knee alignment on clinical outcomes and after TKA. Despite all improvements in conventional intra-medullary and extra-medullary instrumentations, use of intraoperative computer navigation technologies and patient specific instrumentations variability in component alignment is still observed and some patients continue to experience complications such as pain, stiffness, and decreased range of motion after TKA. (15) Patient specific instrumentations are relatively new and have proposed to have several advantages over conventional instrumentations; improved component precision and decreasing outliers. Patient-specific instrumentations have proposed to restore the knee alignment, either the mechanical axis or the kinematic alignment. Several studies (16,17) have also compared patient specific instrumentations while being kinematically aligned with conventional instrumentation. But these studies might have some bias due to small sample size, inadequate radiographic analysis and absence of a comparable control group. Our study had some potential limitations. First, whole length alignment view is the traditional gold standard for coronal alignment assessments of TKA(18). However, according to the introduction of three-dimensional imaging and computer-assisted navigations, sagittal and axial alignment could be evaluated with additional focus. (19,20) Post-operative CT-scan or MRI are usually acquired to assess rotation of the components in patellar mal-tracking cases (7), but it could not be routinely performed for all the patients in large-scale studies regarding expenses with MRI and radiologic exposure with CT-scan. So we could not assess rotational alignment which, could be an important issue regarding long-term survivorship of the implants. Second, in this study skilled surgeon with extensive experience with both PSI and MI systems has performed the TKAs. As with any new system, there is a learning curve with PSIs, and whether less experienced surgeons are able to gain same results, remains to be seen. Third, this study has only evaluated one patient-specific instrumentation design and our results might not be applicable to the other designs, which are currently available. Fourth, the main purpose of any medical intervention is patient's satisfaction. In this study we did not to examine these parameters such as outcome scoring systems, range of motion and length of hospitalization, but there are some evidence representing, better function and quality of life is associated with improved alignment. (3,21) However, to present all these outcomes, long-term follow-up is needed and further studies are required. Fifth, Power analysis was not performed in advance, as this study was a pilot to evaluate and compare PSI with MI. We are currently participating patients in a randomized prospective study on a larger scale. Recent studies have evaluated the idea of a coronal safe zone and associated durability. Parratte et al. (22) compared 292 TKAs with aligned mechanical axis to 106 mal-aligned (± 3°) TKAs, their study showed, aligned TKAs did not have significant advantage. Matziolis et al. (23) presented no difference in patient outcomes between aligned TKA and a subset of varus outliers, having no revisions in either group. However, their findings have not declined the importance of coronal alignment, but the benefits lie along other factors, like soft tissue balance, which could dominate subtle perfections in alignment if not being well optimized. We found the percentage of overall mechanical axis outliers have no significant difference using PSI or MI. The tibial and femoral component outliers for both PSI (6.8%, 10.3%) and MI (12%, 14.8%) in this study were lower than those in a meta-analysis by Mason JB et al (24) for MI (20%, 34%) but higher than those using computer-assisted navigation (5%, 10%). Sagittal alignment is also very important in TKA prognosis. But there has been less attention on parameters of ideal orientation in axial plane than coronal. (19). In this study we have presented, outcomes hava no superiority in sagittal plane either using PSI or MI. We found, the use of PSI has significantly reduced the duration of the surgery and tourniquet time. Minnema B et al (11) showed, as the duration of the surgery increases the risk of infection at the surgical site will increase. While accurate and precise alignment instruments are important in restoring the appropriate overall mechanical axis, they could never be substituted for careful preoperative planning, clinical judgment of surgeon, soft tissue balancing, and accurate implantation technique. TKA performance and patient satisfaction are affected by many factors, neutral coronal and sagittal alignment is only a tool in hands of a surgeon to measure technical success. Our findings demonstrate the accuracy and precision in overall coronal and sagittal alignment has no significant difference in PSI with MI, while the duration of the surgery and tourniquet time is significantly less and the femoral medulla remains intact while using PSIs.

    Samih Tarabichi MD
    Chairman, Tarabichi Joint Replacement Institute, Dubai, UAE


    Usame Hassan Saleh MD
    Orthopaedic Surgeon, Tarabichi Joint Replacement Institute, Dubai, UAE


    Ali Sina Shahi MD
    Postdoctrate Research Fellow, Rothman Institue, PA, USA


    None declared.


    Financial disclosure:
    None declared.



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