Is There Material Loss at the Conical Junctions of Modular Components for Total Knee Arthroplasty?

BACKGROUND: Clinical concern exists regarding fretting corrosion and material loss from taper junctions in orthopedic devices, with previous research focusing on the modular components from total hip arthroplasty. Comparatively little has been published regarding the fretting corrosion and material loss in modular knee devices. The purpose of this study is to evaluate fretting corrosion damage and quantify material loss for conical total knee arthroplasty taper interfaces. METHODS: Stem tapers of 166 retrieved modular knee devices were evaluated for fretting corrosion using a semiquantitative scoring method. High precision profilometry was then used to determine volumetric material loss and maximum wear depth for a subset of 37 components (implanted for 0.25-18.76 years). Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the observed damage. RESULTS: Mild to severe fretting corrosion was observed on the majority of tapers, with 23% receiving a maximum visually determined damage score of 4. The median rate of volumetric material loss was 0.11 mm3/y (range 0.00-0.76) for femoral components (both cone and bore taper surfaces combined) and 0.01 mm3 (range 0.00-8.10) for tibial components. Greater rates of material loss were associated with mixed metal pairings. There was a strong correlation between visual fretting corrosion score and calculated material loss (ρ = 0.68, P < .001). Scanning electron microscopy revealed varying degrees of scratching, wear, fretting corrosion, and instances of cracking with morphology not consistent with fretting corrosion, wear, or fatigue. CONCLUSION: Although visual evidence of fretting corrosion damage was prevalent and correlated with taper material loss, the measured volumetric material loss was low compared with prior reports from total hip arthroplasty.

Are Ceramic Bearings Becoming Cost-Effective for All Patients Within a 90-Day Bundled Payment Period?

BACKGROUND: We analyzed whether the total hospital cost in a 90-day bundled payment period for ceramic-on-polyethylene (C-PE) and ceramic-on-ceramic (COC) total hip arthroplasty (THA) bearings was changing over time, and whether the cost differential between ceramic bearings and metal-on-polyethylene (M-PE) bearings was approaching the previously published tipping point for cost-effectiveness of US$325. METHODS: A total of 245,077 elderly Medicare patients (65+) who underwent primary THA between 2010 and 2015 were identified from the United States Medicare 100% national administrative hospital claims database. The total inpatient cost, calculated up to 90 days after index discharge, was computed using cost-to-charge ratios, and hospital payment was analyzed. The differential total inpatient cost of C-PE and COC bearings, compared to metal-on-polyethylene (M-PE), was evaluated using parametric and nonparametric models. RESULTS: After adjustment for patient and clinical factors, and the year of surgery, the mean hospital cost up to 90 days for primary THA with C-PE or COC was within ±1% of the cost for primary THA with M-PE bearings (P < .001). From the nonparametric analysis, the median total hospital cost was US$296-US$353 more for C-PE and COC than M-PE. Cost differentials were found to decrease significantly over time (P < .001). CONCLUSION: Patient and clinical factors had a far greater impact on the total cost of inpatient THA surgery than bearing selection, even when including readmission costs up to 90 days after discharge. Our findings indicate that the cost-effectiveness thresholds for ceramic bearings relative to M-PE are changing over time and increasingly achievable for the Medicare population.

Does Timing of Primary Total Hip Arthroplasty Prior to or After Lumbar Spine Fusion Have an Effect on Dislocation and Revision Rates?

BACKGROUND: Patients undergoing primary total hip arthroplasty (THA) following lumbar spine fusion have an increased incidence of dislocation compared to those without prior lumbar fusion. The purpose of this study is to determine if timing of THA prior to or after lumbar fusion would have an effect on dislocation and revision incidence in patients with both hip and lumbar spine pathology. METHODS: One hundred percent Medicare inpatient claims data from 2005 to 2015 were used to compare dislocation and revision risks in patients with primary THA with pre-existing lumbar spine fusion vs THA with subsequent lumbar spine fusion within 1, 2, and 5 years after the index THA. A total of 42,300 patients met inclusion criteria, 28,668 patients of which underwent THA with pre-existing lumbar spinal fusion (LSF) and 13,632 patients who had prior THA and subsequent LSF. Patients who had THA first followed by LSF were further stratified based on the interval between index THA and subsequent LSF (1, 2, and 5 years), making 4 total groups for comparison. Multivariate cox regression analysis was performed adjusting for age, socioeconomic status, race, census region, gender, Charlson score, pre-existing conditions, discharge status, length of stay, and hospital characteristics. RESULTS: Patients with prior LSF undergoing THA had a 106% increased risk of dislocation compared to those with LSF done 5 years after THA (P < .001). Risk of revision THA was greater in the pre-existing LSF group by 43%, 41%, and 49% at 1, 2, and 5 years post THA compared to the groups with THA done first with subsequent LSF. Dislocation was the most common etiology for revision THA in all groups, but significantly higher in the prior LSF group (26.6%). CONCLUSION: Results of this study demonstrate that sequence of surgical intervention for concomitant lumbar and hip pathology requiring LSF and THA respectively significantly impacts the fate of the THA performed. Patients with prior LSF undergoing THA are at significantly higher risk of dislocation and subsequent revision compared to those with THA first followed by delayed LSF. LEVEL OF EVIDENCE: 3.

Does Prior Bariatric Surgery Affect Implant Survivorship and Complications Following Primary Total Hip Arthroplasty/Total Knee Arthroplasty?

BACKGROUND: The purpose of this study is to evaluate the impact of prior bariatric surgery on survivorship, outcome, and complications following primary total hip arthroplasty (THA)/total knee arthroplasty (TKA). METHODS: Using the Medicare 5% part B data from 1999 to 2012, we analyzed patients who underwent primary THA (n = 47,895) and primary TKA (n = 86,609). Patients with prior bariatric surgery before arthroplasty were compared to patients with other common metabolic conditions. Kaplan-Meier risk of revision THA/TKA for those with and without bariatric surgery and each of the metabolic bone conditions was calculated. The risk for infection was also evaluated. Regression analysis was used to determine the relative risk of revision at various time intervals for those with and without each of the metabolic conditions. Analysis was also adjusted for the metabolic conditions, age, gender, socioeconomic status, and Charlson comorbidity index. RESULTS: The prevalence of patients with prior bariatric surgery within 24 months of primary THA/TKA was 0.1%. Benchmarked against other common chronic metabolic conditions, bariatric surgery prior to THA was not associated with an increased risk for revision surgery at all measured intervals but positively correlated with increased risk for developing infections. Conversely, patients undergoing primary TKA following bariatric surgery were at increased risk for revision compared to controls but not at increased risk for infection. CONCLUSION: The impact of bariatric surgery prior to elective THA/TKA remains unclear. These patients remain at increased risk for infections following THA and revisions following TKA.

Are Ceramic Bearings Becoming Cost-Effective for All Patients?

BACKGROUND: The purpose of this study is to analyze whether the cost for ceramic-on-polyethylene (C-PE) and ceramic-on-ceramic (COC) bearings used in primary total hip arthroplasty (THA) was changing over time, and if the cost differential between ceramic bearings and metal-on-polyethylene (M-PE) bearings was approaching the previously published tipping point for cost-effectiveness of $325. METHODS: A total of 245,077 elderly Medicare patients (65+) who underwent primary THA between 2010 and 2015 were identified from the United States Medicare 100% national administrative hospital claims database. The inpatient hospital cost, calculated using cost-to-charge ratios, and hospital payment were analyzed. The differential cost of C-PE and COC bearings, compared to M-PE, were evaluated using parametric and nonparametric models. RESULTS: After adjustment for patient and clinical factors, and the year of surgery, the mean hospital cost and payments for primary THA with a C-PE or COC was within ±1% of the cost for primary THA with M-PE bearings (P < .001). From the nonparametric analysis, the median hospital cost was $318-$360 more for C-PE and COC than M-PE. The differential in median Medicare payment for THA with ceramic bearings compared to M-PE was <$100. Cost differentials were found to decrease significantly over time (P < .001). CONCLUSION: Patient and clinical factors had a far greater impact on the cost of inpatient THA surgery than bearing selection. Because we found that costs and cost differentials for ceramic bearings were decreasing over time, and approaching the tipping point, it is likely that the cost-effectiveness thresholds relative to M-PE are likewise changing over time and should be revisited in light of this study.

Total Hip Arthroplasty in Patients With Previous Lumbar Fusion Surgery: Are There More Dislocations and Revisions?

BACKGROUND: The purpose of this study was to determine whether the risk of dislocation and/or revision following THA is increased in patients with a history of prior lumbar fusion given the alterations in dynamic pelvic motion following LSF. METHODS: A total of 62,387 patients (5% Medicare part B claims database) were identified from 1997 to 2014 with primary THA. From this group, 1809 patients (2.9%) were stratified to identify those with prior lumbar fusion within 5 years of primary THA to compare risk of dislocation and revision with those without lumbar fusion. Multivariate cox regression analysis was performed adjusting for age, socioeconomic status, race, census, region, gender, Charlson score, preexisting conditions, and type of fusion. RESULTS: Between years 2002 and 2014, there was a 293% increase in the number of patients with prior lumbar fusion undergoing THA. Prevalence of hip dislocation in patients with lumbar fusion before THA was 7.4% compared to 4.8% without fusion, P < .001. There was an 80% increase in dislocation in the fusion group at 6 months, 71% at 1 year, and 60% at 2 years. There was a 48% increased risk of failure leading to revision hip surgery in patients with fusion at 6 months, 41% at 1 year, and 47% at 2 years. Dislocation was the most common mode of failure leading to revision in both the fusion group (20.8%) and the nonfusion group (16%). CONCLUSION: Results of this study demonstrate that lumbar fusion before THA is an independent risk factor for dislocation leading to increased risk of revision THA.

Complications After Revision Total Hip Arthroplasty in the Medicare Population.

BACKGROUND: The purpose of this study was to identify the incidence and types of complications after revision total hip arthroplasty (THA) within the first year, and determine the relative risk factors for these complications and of re-revision. METHODS: The sample size of 5% Medicare claims data from 1998-2011 was studied. Primary THA patients who underwent subsequent revision were identified using ICD-9-CM codes. Outcomes and complications after revision THA were assessed. Multivariate Cox regression was used to evaluate the effect of patient demographic characteristics on the adjusted complication risk for revision THA patients. RESULTS: Of the 64,260 primary THA patients identified between 1998 and 2011, 3555 patients (5.71%) underwent revision THA. Etiology of primary hip failure included mechanical complications such as loosening and wear (40.7%), dislocation (14.0%), and infection (11.3%). Complications after revision THA included infection and redo revision, 17.3% and 15.8% followed by venous thromboembolic disease (VTE) at 11.1%, dislocation at 5.43%, PE at 3.24%, and death at 2.11%. The rate of "new" infections after an aseptic revision was 8.13%. Patients in the 85+-year-old age group had a 100% greater adjusted risk of VTE (P < .001) and 406% higher adjusted risk of death (P < .001) than those in the 65-69 years-old age group. Patients with higher Charlson scores had higher adjusted risks of VTE (P < .001), infection (P < .001), death (P = .002), and re-revision THA (P = .011). CONCLUSION: Advanced age is a clear risk factor for VTE and mortality, but not for dislocation, infection, or re-revision. Higher Charlson index was found to be a risk factor for every complication after revision except dislocation. Greater attention is required to address the high rate of infection and re-do revision after revision THA (17.3% and 15.8%).

High Risk of Readmission in Octogenarians Undergoing Primary Hip Arthroplasty.

BACKGROUND: As life expectancy increases, more elderly patients with end-stage hip arthritis are electing to undergo primary THA. Octogenarians undergoing THA have more comorbidities than younger patients, but this is not reflected in risk adjustment models for bundled care programs. The burden of care associated with THA in octogenarians has not been well characterized, and doing so may help these value-based programs make adjustments so that this vulnerable patient population does not risk losing access under accountable care models. QUESTIONS/PURPOSES: The purpose of this study was to describe care use, comorbidities, and complications among octogenarians undergoing primary THA. METHODS: Five percent of the Medicare national administrative claims data was queried to identify patients diagnosed with hip osteoarthritis between January 1, 1998, and December 31, 2013. Patients who underwent primary THA were identified and followed longitudinally during the study period using their unique, encrypted Medicare beneficiary identifiers. We compared risk factors and complications between the octogenarian group versus those aged 65 to 69 years. Multivariate Cox regression was used to evaluate the effect of patient/hospital factors on risk of revision, periprosthetic joint infection, dislocation, venous thromboembolism (VTE), and mortality. Patient factors in the model included age, sex, race, region, socioeconomic status, and health status based on Charlson comorbidity score 12 months before replacement surgery. RESULTS: There were 11,960 THAs in the octogenarians in 1998, which increased to 21,620 in 2013, an 81% increase during this study period. Octogenarians were more likely to have a Charlson score of 3 or higher than those patients aged 65 to 69 years (30% versus 17%, odds ratio [OR] 2.07 [1.98-2.20]; p < 0.001), and they were more likely to have coronary artery disease or congestive heart failure (47% versus 29%, OR 2.16 [2.06-2.26]; p < 0.001). The octogenarian group had a greater risk of dislocation (+12%, p = 0.01), VTE (+14%, p < 0.001), and mortality (+150%, p < 0.001) compared with the younger age cohort. A total of 21% of the octogenarians were readmitted after surgery compared with 12% for patients in the younger group (OR=1.64, 95% confidence interval 1.54-1.75; p < 0.001). CONCLUSIONS: Because octogenarians are at increased risk of dislocation, VTE, medical complications, and mortality after THA, value-based care models that penalize hospitals for readmissions and complications may inadvertently result in loss of access to care for this group of patients as a result of the financial makeup of these bundled care models. Value-based care models were developed to improve care and decrease healthcare costs but may have unintended consequences in the octogenarian with higher complication and readmission risks. Financial losses may lead to institutions from withdrawing from the Bundled Payments for Care Improvement program. To try to prevent this from happening to this vulnerable patient population, bundled care programs should evolve and be modified to allow for risk stratification in the overall payment formula to account for increased age and comorbid conditions to ensure continued successful participation in the program among all the stakeholders. LEVEL OF EVIDENCE: Level III, therapeutic study.

Outcomes of Ceramic Bearings After Primary Total Hip Arthroplasty in the Medicare Population.

BACKGROUND: The purpose of this study was to analyze the outcomes of ceramic bearings used in primary total hip arthroplasty (THA) in the Medicare population. METHODS: A total of 315,784 elderly Medicare patients (65+) who underwent primary THA between 2005 and 2014 were identified from the United States Medicare 100% national administrative hospital claims database. Outcomes of interest included infection, dislocation, revision, or mortality at any time point after primary surgery. Propensity scores were developed to adjust for selection bias in the choice of bearing type at index primary surgery. RESULTS: For primary THA patients treated with ceramic-on-polyethylene (C-PE) bearings and ceramic-on-ceramic (COC) bearings, there was significantly reduced risk of infection relative to metal-on-polyethylene (M-PE) bearings (C-PE hazard ratio [HR]: 0.86, P = .001; COC HR: 0.74, P = .01). For the C-PE cohort, we also observed reduced risk of dislocation (HR: 0.81, P < .001) and mortality (HR: 0.92, P < .001). There was no significant difference in risk of revision for either the C-PE or COC bearing cohorts when compared with M-PE. For the COC cohort, there was no significant difference in dislocation or mortality risk. CONCLUSION: As in previous studies, we found that ceramic bearings have similar overall revision risk as M-PE bearings in primary THA at 8-9 years of follow-up. The results indicate that, after adjusting for selection bias and various confounding patient-, surgeon-, and hospital-related factors, Medicare primary THA patients treated with ceramic bearings exhibit lower risk of infection than those treated with M-PE bearings. In addition, C-PE bearings were associated with lower risk of dislocation and mortality.

The Biotribology of PEEK-on-HXLPE Bearings Is Comparable to Traditional Bearings on a Multidirectional Pin-on-disk Tester.

BACKGROUND: All-polymer bearings involving polyetheretherketone (PEEK) have been proposed for orthopaedic applications because they may reduce stress shielding, reduce weight of the implants, reduce wear and risk of osteolysis, and prevent release of metal ions by replacing the metal articulating components. Little is known about the biotribology of all-polymer PEEK bearings, including the effects of cross-shear, which are relevant for implant longevity, especially in the hip, and increased temperature that may affect lubricant proteins and, hence, lubrication in the joint. QUESTIONS/PURPOSES: Using pin-on-disk in vitro testing, we asked: (1) Can all-polymer bearing couples involving PEEK have a comparable or lower wear rate than highly crosslinked UHMWPE (HXLPE) on CoCr bearing couples? (2) Is the wear rate of PEEK bearing couples affected by the amount of cross-shear? (3) Is there a difference in wear mechanism and surface morphology for all-polymer bearing surfaces compared with UHMWPE (HXLPE) on CoCr? METHODS: We simultaneously tested a total of 100 pin-on-disk couples (n = 10 per bearing couple) consisting of three traditional metal-on-UHMWPE and seven polymer-on-polymer bearings for 2 million cycles under physiologically relevant conditions and in accordance with ASTM F732. Using analysis of variance, we analyzed the effect of bearing surface topography and cross-shear on wear rate. The changes in surface topography were evaluated using optical microscopy. Sample size was sufficient to provide 80% power to detect a difference of 1.4 mm3/MC in average wear rates of bearing couples. RESULTS: The combined wear rates of all-polymer bearing couples were not different than traditional bearing couples. With the numbers available, the PEEK and HXLPE bearing couple had a mean wear rate (WR: mean ± SD) of 0.9 ± 1.1 mm3/MC (95% confidence interval [CI], 0.2-1.5 mm3/MC), which was not different than the wear rate of the CoCr and HXLPE bearing couple (1.6 ± 2.0 mm3/MC; 95% CI, 0.4-2.8 mm3/MC; mean difference = 0.73 mm3/MC, p = 0.36). Bearing couples with PEEK reinforced with a carbon fiber (CFR-PEEK) counterface had higher wear rates (14.5 ± 15.1 mm3/MC; 95% CI, 9.1-20.0 mm3/MC) than bearing couples with a PEEK (5.1 ± 3.7 mm3/MC; 95% CI, 3.7-6.4 mm3/MC) or CoCr (4.1 ± 2.7 mm3/MC; 95% CI, 3.2-5.1 mm3/MC) counterface (mean difference = 9.5 mm3/MC, p < 0.001; and mean difference = 10.4 mm3/MC, p < 0.001, respectively). PEEK and HXLPE were insensitive to the cross-shear scenario in the contact mechanics (WR: 0.3 ± 0.1 mm3/MC for PEEK pins [95% CI, 0.2-0.3 mm3/MC] [representing full cross-shear condition] and 0.0 ± 1.0 mm3/MC for PEEK disks [95% CI, -0.5 to 0.5 mm3/MC] [representing limited cross-shear condition], mean difference = 0.3 mm3/MC, p = 0.23; WR: 1.3 ± 1.0 mm3/MC for HXLPE pins [95% CI, 0.7-1.9 mm3/MC] [full cross-shear] and 2.1 ± 2.2 mm3/MC for HXLPE disks [95% CI, 0.8-3.3 mm3/MC] [limited cross-shear], mean difference = 0.8 mm3/MC, p = 0.24). Qualitatively, the surface morphology of UHMWPE appeared similar with PEEK or CoCr as a counterface, although it had a rougher appearance when coupled with carbon fiber-reinforced PEEK. No transfer film was detected on the specimens. CONCLUSIONS: Our in vitro pin-on-disk data suggest that all-polymer bearings, especially PEEK-on-HXLPE bearing couples, may represent a viable alternative to traditional bearings with respect to their wear performance. Our results warrant further testing of all-polymer bearing couples in physiologically relevant joint simulator tests. CLINICAL RELEVANCE: The in vitro pin-on-disk wear resistance of all-polymer bearings incorporating PEEK-on-HXLPE warrants further investigation using joint simulator testing for their validation as useful, metal-free alternatives to traditional CoCr-on-HXLPE bearings for use in orthopaedic applications.

Outcomes of Ceramic Bearings After Revision Total Hip Arthroplasty in the Medicare Population.

BACKGROUND: The purpose of this study was to analyze the utilization and outcomes of ceramic bearings used in revision total hip arthroplasty (R-THA) in the Medicare population. METHODS: A total of 31,809 patients aged >65 years at the time of revision surgery who underwent R-THA between 2005 and 2013 were identified from the United States Medicare 100% national administrative claims database. Outcomes of interest included relative risk of readmission (90 days) or infection, dislocation, rerevision, or mortality at any time point after revision. Propensity scores were developed to adjust for selection bias in the choice of bearing type at revision surgery. RESULTS: The utilization of ceramic-on-polyethylene (C-PE) and ceramic-on-ceramic (COC) bearings in R-THA increased from 5.3% to 26.6% and from 1.8% to 2.5% in between 2005 and 2013, respectively. For R-THA patients treated with C-PE bearings, there was reduced risk of 90-day readmission (hazard ratio, HR: 0.90, P = .007). We also observed a trend for reduced risk of infection with C-PE (HR: 0.88) that did not reach statistical significance (P = .14). For R-THA patients treated with COC bearings, there was reduced risk of dislocation (HR: 0.76, P = .04). There was no significant difference in risk of rerevision or mortality for either the C-PE or COC bearing cohorts when compared with the metal-on-polyethylene bearing cohort. CONCLUSION: Medicare patients treated in a revision scenario with ceramic bearings exhibit similar risk of rerevision, infection, or mortality as those treated with metal-on-polyethylene bearings. Conversely, we found an association between the use of specific ceramic bearings in R-THA and reduced risk of readmission (C-PE) and dislocation (COC).

Effects of gamma and e-beam sterilization on the chemical, mechanical and tribological properties of a novel hydrogel.

Hydrogels are known to possess cartilage-like mechanical and lubrication properties; however, hydrogel sterilization is challenging. Cyborgel(™), a proprietary hydrogel, is intended for use as a cartilage replacement implant. This study evaluated the effect of 30-35 kGy e-beam and gamma radiation on the polymer swell ratio, and the mechanical, chemical and tribological behavior of this hydrogel. Three different formulations were mechanically tested, and material parameters were identified using finite element analysis. FTIR spectroscopy was used to investigate chemical changes. Wear test was carried out for 2 million cycles in bovine serum, followed by 2 million cycles in distilled water. No significant difference was found in the swell ratio, mechanical and tribological properties of control hydrogel samples and those exposed to e-beam or gamma radiation; however, chemical spectra of e-beam sterilized samples revealed minor changes, which were absent in unsterilized and gamma sterilized samples.

Can pin-on-disk testing be used to assess the wear performance of retrieved UHMWPE components for total joint arthroplasty?

The objective of this study was to assess the suitability of using multidirectional pin-on-disk (POD) testing to characterize wear behavior of retrieved ultrahigh molecular weight polyethylene (UHMWPE). The POD wear behavior of 25 UHMWPE components, retrieved after 10 years in vivo, was compared with 25 that were shelf aged for 10-15 years in their original packaging. Components were gamma sterilized (25-40 kGy) in an air or reduced oxygen (inert) package. 9 mm diameter pins were fabricated from each component and evaluated against CoCr disks using a super-CTPOD with 100 stations under physiologically relevant, multidirectional loading conditions. Bovine serum (20 g/L protein concentration) was used as lubricant. Volumetric wear rates were found to vary based on the aging environment, as well as sterilization environment. Volumetric wear rates were the lowest for the pins in the gamma inert, shelf aged cohort. These results support the utility of using modern, multidirectional POD testing with a physiologic lubricant as a novel method for evaluating wear properties of retrieved UHMWPE components. The data also supported the hypothesis that wear rates of gamma-inert liners were lower than gamma-air liners for both retrieved and shelf aging conditions. However, this difference was not statistically significant for the retrieved condition.

Nondestructive assessment of engineered cartilage constructs using near-infrared spectroscopy.

Noninvasive assessment of engineered cartilage properties would enable better control of the developing tissue towards the desired structural and compositional endpoints through optimization of the biochemical environment in real time. The objective of this study is to assess the matrix constituents of cartilage using near-infrared spectroscopy (NIRS), a technique that permits full-depth assessment of developing engineered tissue constructs. Mid-infrared (mid-IR) and NIR data were acquired from full-thickness cartilage constructs that were grown up to 4 weeks with and without mechanical stimulation. Correlations were assessed between established mid-IR peak areas that reflect the relative amount of collagen (amide I, amide II, and 1338 cm(-1)) and proteoglycan (PG), (850 cm(-1)), and the integrated area of the NIR water absorbance at 5190 cm(-1). This analysis was performed to evaluate whether simple assessment of the NIR water absorbance could yield information about matrix development. It was found that an increase in the mid-IR PG absorbance at 850 cm(-1) correlated with the area of the NIR water peak (Spearman's rho = 0.95, p < 0.0001). In the second analysis, a partial least squares method (PLS1) was used to assess whether an extended NIR spectral range (5400-3800 cm(-1)) could be utilized to predict collagen and proteoglycan content of the constructs based on mid-IR absorbances. A subset of spectra was randomly selected as an independent prediction set in this analysis. Average of the normalized root mean square errors of prediction of first-derivative NIR spectral models were 7% for 850 cm(-1) (PG), 11% for 1338 cm(-1) (collagen), 8% for amide II (collagen), and 8% for amide I (collagen). These results demonstrate the ability of NIRS to monitor macromolecular content of cartilage constructs and is the first step towards employing NIR to assess engineered cartilage in situ.